# rlang (development version) Unreleased

## Breaking changes

• If a string is supplied to as_function() instead of an object (function or formula), the function is looked up in the global environment instead of the calling environment. In general, passing a function name as a string is brittle. It is easy to forget to pass the user environment to as_function() and sometimes there is no obvious user environment. The support for strings should be considered a convenience for end users only, not for programmers.

Since environment forwarding is easy to mess up, and since the feature is aimed towards end users, as_function() now defaults to the global environment. Supply an environment explicitly if that is not correct in your case.

• The global .data object now always throws an error when subsetted. This causes early informative errors when the .data pronoun is used outside of a data mask.

We noticed some CRAN failures following this change that revealed issues such as mistakenly using the by argument of dplyr::left_join() or the ... of ggplot2::labs() as data-masked arguments. Since there is no data mask for these arguments, the global .data pronoun (used as a documentation anchor) was subsetted and silently returned NULL.

• For consistency with the cli package, abort(c("Foo", "Bar")) no longer interprets "Bar" as a bullet and it gets displayed as an unprefixed line. You need to be explicit by supplying the "*" specifier: abort(c("Foo", "*" = "Bar")).

• with_handlers() is deprecated.

• call_fn() is deprecated.

## Features and bugfixes

• on_load() and run_on_load() lets you run .onLoad() expressions from any file of your package. on_package_load() runs expressions when another package is loaded. (#1284)

• arg_exclusive() checks that only one argument of a set is supplied (#1261).

• call_name() and call_ns() now fail with calls of the form foo::bar (#670).

• The new predicate is_call_simple() indicates whether a call has a name and/or a namespace. It provides two invariants:

• If is_call_simple(x) is TRUE, call_name() always returns a string.

• If is_call_simple(x, ns = TRUE) is TRUE, call_ns() always returns a string.

• try_catch() is a flexible alternative to both tryCatch() and withCallingHandlers() (#503). It is also more efficient than tryCatch() and creates leaner backtraces.

• entrace() and global_entrace() now log warnings and messages with backtraces attached. Run last_warnings() or last_messages() to inspect the warnings or messages emitted during the last command.

• Objects headers (as printed by last_error(), env_print(), …) are now formatted using the cls class of the cli package.

• global_entrace() is a user-friendly helper for configuring errors in your RProfile. Call it to enrich all base errors with an rlang backtrace with last_error() and backtrace_on_error support.

• arg_match() gains a multiple argument for cases where zero or several matches are allowed (#1281).

• Changes in namespaces are now emboldened in backtraces (#946).

• Functions defined in the global environments or in local execution environments are now displayed with a space separator in backtraces instead of :: and :::. This avoids making it seem like these frame calls are valid R code ready to be typed in (#902).

• Backtraces no longer contain inlined objects to avoid performance issues in edge cases (#1069, r-lib/testthat#1223).

• Condition constructors now check for duplicate field names (#1268).

• as_label() now better handles calls to infix operators (#956, r-lib/testthat#1432). This change improves auto-labelled expressions in data-masking functions like tibble(), mutate(), etc.

• cnd_footer() now returns the footer field by default, if any.

• warn() and inform() now signal conditions of classes "rlang_warning" and "rlang_message" respectively.

• The {{ operator is now detected more strictly (#1087). If additional arguments are supplied through {, it is no longer interpreted as an injection operator.

• The body field of error conditions can now be a character vector.

• External backtraces in error chains are now separately displayed (#1098).

• Trace capture now better handles wrappers of calling handler in case of rethrown chained errors.

• The print() method of rlang errors (commonly invoked with last_error()) has been improved:

• Display calls if present.
• Chained errors are displayed more clearly.
• as_function() gains arg and call arguments to provide contextual information about erroring inputs.

• The error returned by last_error() is now stored on the search path as the .Last.error binding of the "org:r-lib" environment. This is consistent with how the processx package records error conditions. Printing the .Last.error object is now equivalent to running last_error().

• Backtraces now print dangling srcrefs (#1206). Paths are shortened to show only three components (two levels of folder and the file).

• abort() now outputs error messages to stdout in interactive sessions, following the same approach as inform().

• The “Error:” part of error messages is now printed by rlang instead of R. This introduces several cosmetic and informative changes in errors thrown by abort():

• The call field of error messages is now displayed, as is the default in base::stop(). The call is only displayed if it is a simple expression (e.g. no inlined function) and the arguments are not displayed to avoid distracting from the error message. The message is formatted with the tidyverse style (code formatting by the cli package if available).

• The source location is displayed (as in base::stop()) if call carries a source reference. Source locations are not displayed when testthat is running to avoid brittle snapshots.

• If the “Error:” prefix including the call is too long, a line break is introduced to print the error message on the line below. If a source location is displayed in the prefix, a line break is always included.

• The display of chained errors created with the parent argument of abort() has been improved. Chains of errors are now displayed at throw time with the error prefix “Caused by error:”.

• The .ignore_empty argument of enexprs() and enquos() no longer treats named arguments supplied through ... as empty, consistently with exprs() and quos() (#1229).

• is_expression() now returns FALSE for manually constructed expressions that cannot be created by the R parser.

• New C callable rlang_env_unbind(). This is a wrapper around R_removeVarFromFrame() on R >= 4.0.0. On older R this wraps the R function base::rm(). Unlike rm(), this function does not warn (nor throw) when a binding does not exist.

• friendly_type_of() now supports missing arguments.

• env_clone() now properly clones active bindings and avoids forcing promises (#1228). On R < 4.0, promises are still forced.

• Fixed a hang when a quosure inheriting from a data mask is evaluated in the mask again.

• Added is_error(), is_warning(), and is_message() predicates (#1220).

• Fixed an s3_register() issue when the registering package is a dependency of the package that exports the generic (#1225).

• interrupt() no longer fails when interrupts are suspended (#1224).

• Added compat-vctrs.R file for robust manipulation of data frames in zero-deps packages.

• Display of rlang backtraces in dynamic reports (knitted documents and RStudio notebooks) is now controlled by the rlang_backtrace_on_error_report option. By default, nothing is displayed in interactive sessions. In non-interactive sessions, a simplified backtrace is displayed instead of a full backtrace

• The last_error() reminder is no longer displayed in RStudio notebooks.

• abort() and warn() now temporarily set the warning.length global option to the maximum value (8170). The default limit (1000 characters) is especially easy to hit when the message contains a lot of ANSI escapes, as created by the crayon or cli packages (#1211).

• The rlang_trace_top_env global option for trace_back() now detects when backtraces are created within knitr. If the option is not set, its default value becomes knitr::knit_global() when knitr is in progress (as determined from knitr.in.progress global option). This prevents the knitr evaluation context from appearing in the backtraces (#932).

• A knitr::sew() method is registered for rlang_error. This makes it possible to consult last_error() (the call must occur in a different chunk than the error) and to set rlang_backtrace_on_error global options in knitr to display a backtrace on error.

If you show rlang backtraces in a knitted document, also set this in a hidden chunk to trim the knitr context from the backtraces:

options(
rlang_trace_top_env = environment()
)

This change replaces an ad hoc mechanism that caused bugs in corner cases (#1205).

• Internal errors now include a winch backtrace if installed. The user is invited to install it if not installed.

• The root symbol in backtraces is now slightly different so that it can’t be confused with a prompt character (#1207).

• Errors, warnings, and messages generated from rlang are now formatted with cli. This means in practice that long lines are width-wrapped to the terminal size and user themes are applied. This is currently only the case for rlang messages. No formatting is applied when abort(), warn(), and inform() are called from another namespace.

• Added compat-cli.R file to format message elements consistently with cli in zero-deps packages.

• exprs_auto_name() gains a repair_auto argument to make automatic names unique (#1116).

• The .named argument of dots_list() can now be set to NULL to give the result default names. With this option, fully unnamed inputs produce a fully unnamed result with NULL names instead of a character vector of minimal "" names (#390).

• is_named2() is a variant of is_named() that always returns TRUE for empty vectors (#191). It tests for the property that each element of a vector is named rather than the presence of a names attribute.

• check_installed() now consults the rlib_restart_package_not_found global option to determine whether to prompt users to install packages. This also disables the restart mechanism (see below).

• check_installed() now signals errors of class rlib_error_package_not_found with a rlib_restart_package_not_found restart. This allows calling handlers to install the required packages and restart the check (#1150).

• New rlib_bytes class imported from the bench package (#1117). It prints and parses human-friendly sizes.

• The env argument of as_function() now defaults to the global environment. Its previous default was the caller of as_function(), which was rarely the correct environment to look in. Since it’s hard to remember to pass the user environment and it’s sometimes tricky to keep track of it, it’s best to consider string lookup as a convenience for end users, not for developers (#1170).

• The arg_nm argument of arg_match0() must now be a string or symbol.

• inform() and warn() messages can now be silenced with the global options rlib_message_verbosity and rlib_warning_verbosity.

• check_dots_empty(), check_dots_unused(), and check_dots_unnamed() have been moved from ellipsis to rlang. The ellipsis package is deprecated and will eventually be archived.

We have added check_dots_empty0(). It has a different UI but is almost as efficient as checking for missing(...). Use this in very low level functions where a couple microseconds make a difference.

• s3_register() no longer fails when generic does not exist. This prevents failures when users don’t have all the last versions of packages (#1112).

• Formulas are now deparsed according to the tidyverse style guide (~symbol without space and ~ expression() with a space).

• New hash_file(), complementing hash(), to generate 128-bit hashes for the data within a file without loading it into R (#1134).

• New env_cache() function to retrieve a value or create it with a default if it doesn’t exist yet (#1081).

• env_get() and env_get_list() gain a last argument. Lookup stops in that environment. This can be useful in conjunction with base::topenv().

• compat-purrr.R now longer includes pluck* helpers; these used a defintion of pluck that predated purrr (#1159). *_cpl() has also been removed. The map* wrappers now call as_function() so that you can pass short anonymous functions that use ~ (#1157).

• New call_match() function. It is like match.call() but also supports matching missing arguments to their defaults in the function definition (#875).

call_standardise() is deprecated in favour of call_match().

• is_installed() and check_installed() gain a version argument (#1165).

• expr_deparse() now properly escapes \ characters in symbols, argument names, and vector names (#1160).

• friendly_type_of() (from compat-friendly-type.R) now supports matrices and arrays (#141).

• friendly_type() is deprecated and as_pairlist() is defunct.

• Updated env_print() to use format_error_bullets() and consistent tidyverse style (#1154).

• set_names() now recycles names of size 1 to the size of the input, following the tidyverse recycling rules.

• format_error_bullets() now treats:

• Unnamed elements as unindented line breaks (#1130)
• Elements named "v" as green ticks (@rossellhayes)
• Elements named " " as indented line breaks
• Elements named "*" as normal bullets
• Elements named "!" as warning bullets

For convenience, a fully unnamed vector is interpreted as a vector of "*" bullets.

• New function arg_require() to check that an argument is supplied. It produces a more friendly error message than force() (#1118).

• arg_match() now mentions the supplied argument (#1113).

• is_missing() now handles arguments with a default consistently with base::missing() (#1106).

• is_bare_formula() now handles the scoped argument consistently. The default has been changed to TRUE for compatibility with the historical default behaviour (#1115).

• The “definition” API (dots_definitions() etc.) has been archived.

• Fixed !! issue involving binary operators (#1125).

• New is_complex() predicates to complete the family (#1127).

• .data now fails early when it is subsetted outside of a data mask context. This provides a more informative error message (#804, #1133).

• The C function r_obj_address() now properly prefixes addresses with the hexadecimal prefix 0x on Windows (#1135).

• Fixed performance issue when splicing classes that explicitly inherit from list with !!! (#1140, r-lib/vctrs#1170).

• Attributes of quosure lists are no longer modified by side effect (#1142).

• enquo(), enquos() and variants now support numbered dots like ..1 (#1137).

• obj_address() is now exported.

• %<~% now actually works.

• Fixed a bug in the AST rotation algorithm that caused the !! operator to unexpectedly mutate injected objects (#1103).

• XXH3_64bits() from the XXHash library is now exposed as C callable under the name rlang_xxh3_64bits().

# rlang 0.4.11 2021-04-30

• Fix for CRAN checks.

• Fixed a gcc11 warning related to hash() (#1088).

# rlang 0.4.10 2020-12-30

• New hash() function to generate 128-bit hashes for arbitrary R objects using the xxHash library. The implementation is modeled after xxhashlite, created by @coolbutuseless.

• New check_installed() function. Unlike is_installed(), it asks the user whether to install missing packages. If the user accepts, the packages are installed with pak::pkg_install() if available, or utils::install.packages() otherwise. If the session is non interactive or if the user chooses not to install the packages, the current evaluation is aborted (#1075).

• rlang is now licensed as MIT (#1063).

• Fixed an issue causing extra empty lines in inform() messages with .frequency (#1076, @schloerke).

• expr_deparse() now correctly wraps code using :: and ::: (#1072, @krlmlr).

# rlang 0.4.9 2020-11-25

## Breaking changes

• Dropped support for the R 3.2 series.

## New features

• inject() evaluates its argument with !!, !!!, and {{ support.

• New enquo0() and enquos0() operators for defusing function arguments without automatic injection (unquotation).

• format_error_bullets() is no longer experimental. The message arguments of abort(), warn(), and inform() are automatically passed to that function to make it easy to create messages with regular, info, and error bullets. See ?format_error_bullets for more information.

• New zap_srcref() function to recursively remove source references from functions and calls.

• A new compat file for the zeallot operator %<-% is now available in the rlang repository.

• New %<~% operator to define a variable lazily.

• New env_browse() and env_is_browsed() functions. env_browse() is equivalent to evaluating browser() within an environment. It sets the environment to be persistently browsable (or unsets it if value = FALSE is supplied).

• Functions created from quosures with as_function() now print in a more user friendly way.

• New rlang_print_backtrace C callable for debugging from C interpreters (#1059).

## Bugfixes and improvements

• The .data pronoun no longer skips functions (#1061). This solves a dplyr issue involving rowwise data frames and list-columns of functions (tidyverse/dplyr#5608).

• as_data_mask() now intialises environments of the correct size to improve efficiency (#1048).

• eval_bare(), eval_tidy() (#961), and with_handlers() (#518) now propagate visibility.

• cnd_signal() now ignores NULL inputs.

• Fixed bug that prevented splicing a named empty vector with the !!! operator (#1045).

• The exit status of is now preserved in non-interactive sessions when entrace() is used as an options(error = ) handler (#1052, rstudio/bookdown#920).

• next and break are now properly deparsed as nullary operators.

# rlang 0.4.8 2020-10-08

• Backtraces now include native stacks (e.g. from C code) when the winch package is installed and rlang_trace_use_winch is set to TRUE (@krlmlr).

• Compatibility with upcoming testthat 3 and magrittr 2 releases.

• get_env() now returns the proper environment with primitive functions, i.e. the base namespace rather than the base environment (r-lib/downlit#32).

• entrace() no longer handles non-rlang errors that carry a backtrace. This improves compatibility with packages like callr.

• Backtraces of unhandled errors are now displayed without truncation in non-interactive sessions (#856).

• is_interactive() no longer consults “rstudio.notebook.executing” option (#1031).

# rlang 0.4.7 2020-07-09

• cnd_muffle() now returns FALSE instead of failing if the condition is not mufflable (#1022).

• warn() and inform() gain a .frequency argument to control how frequently the warning or message should be displayed.

• New raw_deparse_str() function for converting a raw vector into a string of hexadecimal characters (@krlmlr, #978).

• The backtraces of chained errors are no longer decomposed by error context. Instead, the error messages are displayed as a tree to reflect the error ancestry, and the deepest backtrace in the ancestry is displayed.

This change simplifies the display (#851) and makes it possible to rethow errors from a calling handler rather than an exiting handler, which we now think is more appropriate because it allows users to recover() into the error.

• env_bind(), env_bind_active(), env_bind_lazy(), env_get(), and env_get_list() have been rewritten in C.

• env_poke() now supports zap() sentinels for removing bindings (#1012) and has better support for characters that are not representable in the local encoding.

• env_poke() has been rewritten in C for performance.

• The unicode translation warnings that appeared on Windows with R 4.0 are now fixed.

• env_unbind(inherit = TRUE) now only removes a binding from the first parent environment that has a binding. It used to remove the bindings from the whole ancestry. The new behaviour doesn’t guarantee that a scope doesn’t have a binding but it is safer.

• env_has() is now rewritten in C for performance.

• dots_list() gains a .named argument for auto-naming dots (#957).

• It is now possible to subset the .data pronoun with quosured symbols or strings (#807).

• Expressions like quote(list("a b" = 1)) are now properly deparsed by expr_deparse() (#950).

• parse_exprs() now preserves names (#808). When a single string produces multiple expressions, the names may be useful to figure out what input produced which expression.

• parse_exprs() now supports empty expressions (#954).

• list2(!!!x) no longer evaluates x multiple times (#981).

• is_installed() now properly handles a pkg argument of length > 1. Before this it silently tested the first element of pkg only and thus always returned TRUE if the first package was installed regardless of the actual length of pkg. (#991, @salim-b)

• arg_match0() is a faster version of arg_match() for use when performance is at a premium (#997, @krlmlr).

# rlang 0.4.6 2020-05-02

• !!! now uses a combination of length(), names(), and [[ to splice S3 and S4 objects. This produces more consistent behaviour than as.list() on a wider variety of vector classes (#945, tidyverse/dplyr#4931).

# rlang 0.4.5 2020-03-01

• set_names(), is_formula(), and names2() are now implemented in C for efficiency.

• The .data pronoun now accepts symbol subscripts (#836).

• Quosure lists now explicitly inherit from "list". This makes them compatible with the vctrs package (#928).

• All rlang options are now documented in a centralised place, see ?rlang::faq-options (#899, @smingerson).

• Fixed crash when env_bindings_are_lazy() gets improper arguments (#923).

• arg_match() now detects and suggests possible typos in provided arguments (@jonkeane, #798).

• arg_match() now gives an error if argument is of length greater than 1 and doesn’t exactly match the values input, similar to base match.arg (#914, @AliciaSchep)

# rlang 0.4.4 2020-01-28

• Maintenance release for CRAN.

# rlang 0.4.3 2020-01-24

• You can now use glue syntax to unquote on the LHS of :=. This syntax is automatically available in all functions taking dots with list2() and enquos(), and thus most of the tidyverse. Note that if you use the glue syntax in an R package, you need to import glue.

A single pair of braces triggers normal glue interpolation:


df <- data.frame(x = 1:3)

suffix <- "foo"
df %>% dplyr::mutate("var_{suffix}" := x * 2)
#>   x var_foo
#> 1 1       2
#> 2 2       4
#> 3 3       6

Using a pair of double braces is for labelling a function argument. Technically, this is shortcut for "{as_label(enquo(arg))}". The syntax is similar to the curly-curly syntax for interpolating function arguments:


my_wrapper <- function(data, var, suffix = "foo") {
data %>% dplyr::mutate("{{ var }}_{suffix}" := {{ var }} * 2)
}
df %>% my_wrapper(x)
#>   x x_foo
#> 1 1     2
#> 2 2     4
#> 3 3     6

df %>% my_wrapper(sqrt(x))
#>   x sqrt(x)_foo
#> 1 1    2.000000
#> 2 2    2.828427
#> 3 3    3.464102
• Fixed a bug in magrittr backtraces that caused duplicate calls to appear in the trace.

• Fixed a bug in magrittr backtraces that caused wrong call indices.

• Empty backtraces are no longer shown when rlang_backtrace_on_error is set.

• The tidy eval .env pronoun is now exported for documentation purposes.

• warn() and abort() now check that either class or message was supplied. inform() allows sending empty message as it is occasionally useful for building user output incrementally.

• flatten() fails with a proper error when input can’t be flattened (#868, #885).

• inform() now consistently appends a final newline to the message (#880).

• cnd_body.default() is now properly registered.

• cnd_signal() now uses the same approach as abort() to save unhandled errors to last_error().

• Parsable constants like NaN and NA_integer_ are now deparsed by expr_deparse() in their parsable form (#890).

• Infix operators now stick to their LHS when deparsed by expr_deparse() (#890).

# rlang 0.4.2 2019-11-23

• New cnd_header(), cnd_body() and cnd_footer() generics. These are automatically called by conditionMessage.rlang_error(), the default method for all rlang errors.

Concretely, this is a way of breaking up lazy generation of error messages with conditionMessage() into three independent parts. This provides a lot of flexibility for hierarchies of error classes, for instance you could inherit the body of an error message from a parent class while overriding the header and footer.

• The reminder to call last_error() is now less confusing thanks to a suggestion by @markhwhiteii.

• The functions prefixed in scoped_ have been renamed to use the more conventional local_ prefix. For instance, scoped_bindings() is now local_bindings(). The scoped_ functions will be deprecated in the next significant version of rlang (0.5.0).

• The .subclass argument of abort(), warn() and inform() has been renamed to class. This is for consistency with our conventions for class constructors documented in https://adv-r.hadley.nz/s3.html#s3-subclassing.

• inform() now prints messages to the standard output by default in interactive sessions. This makes them appear more like normal output in IDEs such as RStudio. In non-interactive sessions, messages are still printed to standard error to make it easy to redirect messages when running R scripts (#852).

• Fixed an error in trace_back() when the call stack contains a quosured symbol.

• Backtrace is now displayed in full when an error occurs in non-interactive sessions. Previously the backtraces of parent errors were left out.

# rlang 0.4.1 2019-10-24

• New experimental framework for creating bulleted error messages. See ?cnd_message for the motivation and an overwiew of the tools we have created to support this approach. In particular, abort() now takes character vectors to assemble a bullet list. Elements named x are prefixed with a red cross, elements named i are prefixed with a blue info symbol, and unnamed elements are prefixed with a bullet.

• Capture of backtrace in the context of rethrowing an error from an exiting handler has been improved. The tryCatch() context no longer leaks in the high-level backtrace.

• Printing an error no longer recommends calling last_trace(), unless called from last_error().

• env_clone() no longer recreates active bindings and is now just an alias for env2list(as.list(env)). Unlike as.list() which returns the active binding function on R < 4.0, the value of active bindings is consistently used in all versions.

• The display of rlang errors derived from parent errors has been improved. The simplified backtrace (as printed by rlang::last_error()) no longer includes the parent errors. On the other hand, the full backtrace (as printed by rlang::last_trace()) now includes the backtraces of the parent errors.

• cnd_signal() has improved support for rlang errors created with error_cnd(). It now records a backtrace if there isn’t one already, and saves the error so it can be inspected with rlang::last_error().

• rlang errors are no longer formatted and saved through conditionMessage(). This makes it easier to use a conditionMessage() method in subclasses created with abort(), which is useful to delay expensive generation of error messages until display time.

• abort() can now be called without error message. This is useful when conditionMessage() is used to generate the message at print-time.

• Fixed an infinite loop in eval_tidy(). It occurred when evaluating a quosure that inherits from the mask itself.

• env_bind()’s performance has been significantly improved by fixing a bug that caused values to be repeatedly looked up by name.

• cnd_muffle() now checks that a restart exists before invoking it. The restart might not exist if the condition is signalled with a different function (such as stop(warning_cnd)).

• trace_length() returns the number of frames in a backtrace.

• Added internal utility cnd_entrace() to add a backtrace to a condition.

• rlang::last_error() backtraces are no longer displayed in red.

• x %|% y now also works when y is of same length as x (@rcannood, #806).

• Empty named lists are now deparsed more explicitly as "<named list>".

• Fixed chr() bug causing it to return invisibly.

# rlang 0.4.0 2019-06-25

## Tidy evaluation

### Interpolate function inputs with the curly-curly operator

The main change of this release is the new tidy evaluation operator {{. This operator abstracts the quote-and-unquote idiom into a single interpolation step:

my_wrapper <- function(data, var, by) {
data %>%
group_by({{ by }}) %>%
summarise(average = mean({{ var }}, na.rm = TRUE))
}

{{ var }} is a shortcut for !!enquo(var) that should be easier on the eyes, and easier to learn and teach.

Note that for multiple inputs, the existing documentation doesn’t stress enough that you can just pass dots straight to other tidy eval functions. There is no need for quote-and-unquote unless you need to modify the inputs or their names in some way:

my_wrapper <- function(data, var, ...) {
data %>%
group_by(...) %>%
summarise(average = mean({{ var }}, na.rm = TRUE))
}

### More robust .env pronoun

Another improvement to tidy evaluation should make it easier to use the .env pronoun. Starting from this release, subsetting an object from the .env pronoun now evaluates the corresponding symbol. This makes .env more robust, in particular in magrittr pipelines. The following example would previously fail:

foo <- 10
mtcars %>% mutate(cyl = cyl * .env$foo) This way, using the .env pronoun is now equivalent to unquoting a constant objects, but with an easier syntax: mtcars %>% mutate(cyl = cyl * !!foo) Note that following this change, and despite its name, .env is no longer referring to a bare environment. Instead, it is a special shortcut with its own rules. Similarly, the .data pronoun is not really a data frame. ## New functions and features • New pairlist2() function with splicing support. It preserves missing arguments, which makes it useful for lists of formal parameters for functions. • is_bool() is a scalar type predicate that checks whether its input is a single TRUE or FALSE. Like is_string(), it returns FALSE when the input is missing. This is useful for type-checking function arguments (#695). • is_string() gains a string argument. is_string(x, "foo") is a shortcut for is_character(x) && length(x) == 1 && identical(x, "foo"). • Lists of quosures now have pillar methods for display in tibbles. • set_names() now names unnamed input vectors before applying a function. The following expressions are now equivalent: letters %>% set_names() %>% set_names(toupper) letters %>% set_names(toupper) • You can now pass a character vector as message argument for abort(), warn(), inform(), and signal(). The vector is collapsed to a single string with a "\n" newline separating each element of the input vector (#744). • maybe_missing() gains a default argument. • New functions for weak references: new_weakref(), weakref_key(), weakref_value(), and is_weakref() (@wch, #787). ## Performance • The performance of exec() has been improved. It is now on the same order of performance as do.call(), though slightly slower. • call2() now uses the new pairlist2() function internally. This considerably improves its performance. This also means it now preserves empty arguments: call2("fn", 1, , foo = ) #> fn(1, , foo = ) ## Bugfixes and small improvements • with_handlers() now installs calling handlers first on the stack, no matter their location in the argument list. This way they always take precedence over exiting handlers, which ensures their side effects (such as logging) take place (#718). • In rlang backtraces, the global:: prefix is now only added when the function directly inherits from the global environment. Functions inheriting indirectly no longer have a namespace qualifier (#733). • options(error = rlang::entrace) now has better support for errors thrown from C (#779). It also saves structured errors in the error field of rlang::last_error(). • ns_env() and ns_env_name() (experimental functions) now support functions and environments consisently. They also require an argument from now on. • is_interactive() is aware of the TESTTHAT environment variable and returns FALSE when it is "true" (@jennybc, #738). • fn_fmls() and variants no longer coerce their input to a closure. Instead, they throw an error. • Fixed an issue in knitr that caused backtraces to print even when error = TRUE. • The return object from as_function() now inherits from "function" (@richierocks, #735). ## Lifecycle We commit to support 5 versions of R. As R 3.6 is about to be released, rlang now requires R 3.2 or greater. We’re also continuing our efforts to streamline and narrow the rlang API. • modify() and prepend() (two experimental functions marked as in the questioning stage since rlang 0.3.0) are now deprecated. Vector functions are now out of scope for rlang. They might be revived in the vctrs or funs packages. • exiting() is soft-deprecated because with_handlers() treats handlers as exiting by default. • The vector constructors like lgl() or new_logical() are now in the questioning stage. They are likely to be moved to the vctrs package at some point. Same for the missing values shortcuts like na_lgl. • as_logical(), as_integer(), etc have been soft-deprecated in favour of vctrs::vec_cast(). • type_of(), switch_type(), coerce_type(), and friends are soft-deprecated. • The encoding and locale API was summarily archived. This API didn’t bring any value and wasn’t used on CRAN. • lang_type_of(), switch_lang(), and coerce_lang() were archived. These functions were not used on CRAN or internally. • Subsetting quosures with [ or [[ is soft-deprecated. • All functions that were soft-deprecated, deprecated, or defunct in previous releases have been bumped to the next lifecycle stage. # rlang 0.3.2 2019-03-21 • Fixed protection issue reported by rchk. • The experimental option rlang__backtrace_on_error is no longer experimental and has been renamed to rlang_backtrace_on_error. • New “none” option for rlang_backtrace_on_error. • Unary operators applied to quosures now give better error messages. • Fixed issue with backtraces of warnings promoted to error, and entraced via withCallingHandlers(). The issue didn’t affect entracing via top level options(error = rlang::entrace) handling. # rlang 0.3.1 2019-01-08 This patch release polishes the new backtrace feature introduced in rlang 0.3.0 and solves bugs for the upcoming release of purrr 0.3.0. It also features as_label() and as_name() which are meant to replace quo_name() in the future. Finally, a bunch of deparsing issues have been fixed. ## Backtrace fixes • New entrace() condition handler. Add this to your RProfile to enable rlang backtraces for all errors, including warnings promoted to errors:  if (requireNamespace("rlang", quietly = TRUE)) { options(error = rlang::entrace) } This handler also works as a calling handler:  with_handlers( error = calling(entrace), foo(bar) ) However it’s often more practical to use with_abort() in that case:  with_abort(foo(bar)) • with_abort() gains a classes argument to promote any kind of condition to an rlang error. • New last_trace() shortcut to print the backtrace stored in the last_error(). • Backtrace objects now print in full by default. • Calls in backtraces are now numbered according to their position in the call tree. The numbering is non-contiguous for simplified backtraces because of omitted call frames. • catch_cnd() gains a classes argument to specify which classes of condition to catch. It returns NULL if the expected condition could not be caught (#696). ## as_label() and as_name() The new as_label() and as_name() functions should be used instead of quo_name() to transform objects and quoted expressions to a string. We have noticed that tidy eval users often use quo_name() to extract names from quosured symbols. This is not a good use for that function because the way quo_name() creates a string is not a well defined operation. For this reason, we are replacing quo_name() with two new functions that have more clearly defined purposes, and hopefully better names reflecting those purposes. Use as_label() to transform any object to a short human-readable description, and as_name() to extract names from (possibly quosured) symbols. Create labels with as_label() to: • Display an object in a concise way, for example to labellise axes in a graphical plot. • Give default names to columns in a data frame. In this case, labelling is the first step before name repair. We expect as_label() to gain additional parameters in the future, for example to control the maximum width of a label. The way an object is labelled is thus subject to change. On the other hand, as_name() transforms symbols back to a string in a well defined manner. Unlike as_label(), as_name() guarantees the roundtrip symbol -> string -> symbol. In general, if you don’t know for sure what kind of object you’re dealing with (a call, a symbol, an unquoted constant), use as_label() and make no assumption about the resulting string. If you know you have a symbol and need the name of the object it refers to, use as_name(). For instance, use as_label() with objects captured with enquo() and as_name() with symbols captured with ensym(). Note that quo_name() will only be soft-deprecated at the next major version of rlang (0.4.0). At this point, it will start issuing once-per-session warnings in scripts, but not in packages. It will then be deprecated in yet another major version, at which point it will issue once-per-session warnings in packages as well. You thus have plenty of time to change your code. ## Minor fixes and features • New is_interactive() function. It serves the same purpose as base::interactive() but also checks if knitr is in progress and provides an escape hatch. Use with_interactive() and scoped_interactive() to override the return value of is_interactive(). This is useful in unit tests or to manually turn on interactive features in RMarkdown outputs • calling() now boxes its argument. • New done() function to box a value. Done boxes are sentinels to indicate early termination of a loop or computation. For instance, it will be used in the purrr package to allow users to shortcircuit a reduction or accumulation. • new_box() now accepts additional attributes passed to structure(). • Fixed a quotation bug with binary operators of zero or one argument such as /(1) (#652). They are now deparsed and printed properly as well. • New call_ns() function to retrieve the namespace of a call. Returns NULL if the call is not namespaced. • Top-level S3 objects are now deparsed properly. • Empty { blocks are now deparsed on the same line. • Fixed a deparsing issue with symbols containing non-ASCII characters (#691). • expr_print() now handles [ and [[ operators correctly, and deparses non-syntactic symbols with backticks. • call_modify() now respects ordering of unnamed inputs. Before this fix, it would move all unnamed inputs after named ones. • as_closure() wrappers now call primitives with positional arguments to avoid edge case issues of argument matching. • as_closure() wrappers now dispatch properly on methods defined in the global environment (tidyverse/purrr#459). • as_closure() now supports both base-style (e1 and e2) and purrr-style (.x and .y) arguments with binary primitives. • exec() takes .fn as first argument instead of f, for consistency with other rlang functions. • Fixed infinite loop with quosures created inside a data mask. • Base errors set as parent of rlang errors are now printed correctly. # rlang 0.3.0 2018-10-22 ## Breaking changes The rlang API is still maturing. In this section, you’ll find hard breaking changes. See the life cycle section below for an exhaustive list of API changes. • quo_text() now deparses non-syntactic symbols with backticks: quo_text(sym("foo+")) #> [1] "foo+" This caused a number of issues in reverse dependencies as quo_text() tends to be used for converting symbols to strings. quo_text() and quo_name() should not be used for this purpose because they are general purpose deparsers. These functions should generally only be used for printing outputs or creating default labels. If you need to convert symbols to strings, please use as_string() rather than quo_text(). We have extended the documentation of ?quo_text and ?quo_name to make these points clearer. • exprs() no longer flattens quosures. exprs(!!!quos(x, y)) is now equivalent to quos(x, y). • The sentinel for removing arguments in call_modify() has been changed from NULL to zap(). This breaking change is motivated by the ambiguity of NULL with valid argument values.  call_modify(call, arg = NULL) # Add arg = NULL to the call call_modify(call, arg = zap()) # Remove the arg argument from the call • The %@% operator now quotes its input and supports S4 objects. This makes it directly equivalent to @ except that it extracts attributes for non-S4 objects (#207). • Taking the env_parent() of the empty environment is now an error. ## Summary The changes for this version are organised around three main themes: error reporting, tidy eval, and tidy dots. • abort() now records backtraces automatically in the error object. Errors thrown with abort() invite users to call rlang::last_error() to see a backtrace and help identifying where and why the error occurred. The backtraces created by rlang (you can create one manually with trace_back()) are printed in a simplified form by default that removes implementation details from the backtrace. To see the full backtrace, call summary(rlang::last_error()). abort() also gains a parent argument. This is meant for situations where you’re calling a low level API (to download a file, parse a JSON file, etc) and would like to intercept errors with base::tryCatch() or rlang::with_handlers() and rethrow them with a high-level message. Call abort() with the intercepted error as the parent argument. When the user prints rlang::last_error(), the backtrace will be shown in two sections corresponding to the high-level and low-level contexts. In order to get segmented backtraces, the low-level error has to be thrown with abort(). When that’s not the case, you can call the low-level function within with_abort() to automatically promote all errors to rlang errors. • The tidy eval changes are mostly for developers of data masking APIs. The main user-facing change is that .data[[ is now an unquote operator so that var in .data[[var]] is never masked by data frame columns and always picked from the environment. This makes the pronoun safe for programming in functions. • The !!! operator now supports all classed objects like factors. It calls as.list() on S3 objects and as(x, "list") on S4 objects. • dots_list() gains several arguments to control how dots are collected. You can control the selection of arguments with the same name with .homonyms (keep first, last, all, or abort). You can also elect to preserve empty arguments with .preserve_empty. ## Conditions and errors • New trace_back() captures a backtrace. Compared to the base R traceback, it contains additional structure about the relationship between frames. It comes with tools for automatically restricting to frames after a certain environment on the stack, and to simplify when printing. These backtraces are now recorded in errors thrown by abort() (see below). • abort() gains a parent argument to specify a parent error. This is meant for situations where a low-level error is expected (e.g. download or parsing failed) and you’d like to throw an error with higher level information. Specifying the low-level error as parent makes it possible to partition the backtraces based on ancestry. • Errors thrown with abort() now embed a backtrace in the condition object. It is no longer necessary to record a trace with a calling handler for such errors. • with_abort() runs expressions in a context where all errors are promoted to rlang errors and gain a backtrace. • Unhandled errors thrown by abort() are now automatically saved and can be retrieved with rlang::last_error(). The error prints with a simplified backtrace. Call summary(last_error()) to see the full backtrace. • New experimental option rlang__backtrace_on_error to display backtraces alongside error messages. See ?rlang::abort for supported options. • The new signal() function completes the abort(), warn() and inform() family. It creates and signals a bare condition. • New interrupt() function to simulate an user interrupt from R code. • cnd_signal() now dispatches messages, warnings, errors and interrupts to the relevant signalling functions (message(), warning(), stop() and the C function Rf_onintr()). This makes it a good choice to resignal a captured condition. • New cnd_type() helper to determine the type of a condition ("condition", "message", "warning", "error" or "interrupt"). • abort(), warn() and inform() now accepts metadata with .... The data are stored in the condition and can be examined by user handlers. Consequently all arguments have been renamed and prefixed with a dot (to limit naming conflicts between arguments and metadata names). • with_handlers() treats bare functions as exiting handlers (equivalent to handlers supplied to tryCatch()). It also supports the formula shortcut for lambda functions (as in purrr). • with_handlers() now produces a cleaner stack trace. ## Tidy dots • The input types of !!! have been standardised. !!! is generally defined on vectors: it takes a vector (typically, a list) and unquotes each element as a separate argument. The standardisation makes !!! behave the same in functions taking dots with list2() and in quoting functions. !!! accepts these types: • Lists, pairlists, and atomic vectors. If they have a class, they are converted with base::as.list() to allow S3 dispatch. Following this change, objects like factors can now be spliced without data loss. • S4 objects. These are converted with as(obj, "list") before splicing. • Quoted blocks of expressions, i.e. { } calls !!! disallows: • Any other objects like functions or environments, but also language objects like formula, symbols, or quosures. Quoting functions used to automatically wrap language objects in lists to make them spliceable. This behaviour is now soft-deprecated and it is no longer valid to write !!!enquo(x). Please unquote scalar objects with !! instead. • dots_list(), enexprs() and enquos() gain a .homonyms argument to control how to treat arguments with the same name. The default is to keep them. Set it to "first" or "last" to keep only the first or last occurrences. Set it to "error" to raise an informative error about the arguments with duplicated names. • enexprs() and enquos() now support .ignore_empty = "all" with named arguments as well (#414). • dots_list() gains a .preserve_empty argument. When TRUE, empty arguments are stored as missing arguments (see ?missing_arg). • dots_list(), enexprs() and enquos() gain a .check_assign argument. When TRUE, a warning is issued when a <- call is detected in .... No warning is issued if the assignment is wrapped in brackets like { a <- 1 }. The warning lets users know about a possible typo in their code (assigning instead of matching a function parameter) and requires them to be explicit that they really want to assign to a variable by wrapping in parentheses. • lapply(list(quote(foo)), list2) no longer evaluates foo (#580). ## Tidy eval • You can now unquote quosured symbols as LHS of :=. The symbol is automatically unwrapped from the quosure. • Quosure methods have been defined for common operations like ==. These methods fail with an informative error message suggesting to unquote the quosure (#478, #tidyverse/dplyr#3476). • as_data_pronoun() now accepts data masks. If the mask has multiple environments, all of these are looked up when subsetting the pronoun. Function objects stored in the mask are bypassed. • It is now possible to unquote strings in function position. This is consistent with how the R parser coerces strings to symbols. These two expressions are now equivalent: expr("foo"()) and expr((!!"foo")()). • Quosures converted to functions with as_function() now support nested quosures. • expr_deparse() (used to print quosures at the console) now escapes special characters. For instance, newlines now print as "\n" (#484). This ensures that the roundtrip parse_expr(expr_deparse(x)) is not lossy. • new_data_mask() now throws an error when bottom is not a child of top (#551). • Formulas are now evaluated in the correct environment within eval_tidy(). This fixes issues in dplyr and other tidy-evaluation interfaces. • New functions new_quosures() and as_quosures() to create or coerce to a list of quosures. This is a small S3 class that ensures two invariants on subsetting and concatenation: that each element is a quosure and that the list is always named even if only with a vector of empty strings. ## Environments • env() now treats a single unnamed argument as the parent of the new environment. Consequently, child_env() is now superfluous and is now in questioning life cycle. • New current_env() and current_fn() functions to retrieve the current environment or the function being evaluated. They are equivalent to base::environment() and base::sys.function() called without argument. • env_get() and env_get_list() gain a default argument to provide a default value for non-existing bindings. • env_poke() now returns the old value invisibly rather than the input environment. • The new function env_name() returns the name of an environment. It always adds the “namespace:” prefix to namespace names. It returns “global” instead of “.GlobalEnv” or “R_GlobalEnv”, “empty” instead of “R_EmptyEnv”. The companion env_label() is like env_name() but returns the memory address for anonymous environments. • env_parents() now returns a named list. The names are taken with env_name(). • env_parents() and env_tail() now stop at the global environment by default. This can be changed with the last argument. The empty environment is always a stopping condition so you can take the parents or the tail of an environment on the search path without changing the default. • New predicates env_binding_are_active() and env_binding_are_lazy() detect the kind of bindings in an environment. • env_binding_lock() and env_binding_unlock() allows to lock and unlock multiple bindings. The predicate env_binding_are_locked() tests if bindings are locked. • env_lock() and env_is_locked() lock an environment or test if an environment is locked. • env_print() pretty-prints environments. It shows the contents (up to 20 elements) and the properties of the environment. • is_scoped() has been soft-deprecated and renamed to is_attached(). It now supports environments in addition to search names. • env_bind_lazy() and env_bind_active() now support quosures. • env_bind_exprs() and env_bind_fns() are soft-deprecated and renamed to env_bind_lazy() and env_bind_active() for clarity and consistency. • env_bind(), env_bind_exprs(), and env_bind_fns() now return the list of old binding values (or missing arguments when there is no old value). This makes it easy to restore the original environment state: old <- env_bind(env, foo = "foo", bar = "bar") env_bind(env, !!!old) • env_bind() now supports binding missing arguments and removing bindings with zap sentinels. env_bind(env, foo = ) binds a missing argument and env_bind(env, foo = zap()) removes the foo binding. • The inherit argument of env_get() and env_get_list() has changed position. It now comes after default. • scoped_bindings() and with_bindings() can now be called without bindings. • env_clone() now recreates active bindings correctly. • env_get() now evaluates promises and active bindings since these are internal objects which should not be exposed at the R level (#554) • env_print() calls get_env() on its argument, making it easier to see the environment of closures and quosures (#567). • env_get() now supports retrieving missing arguments when inherit is FALSE. ## Calls • is_call() now accepts multiple namespaces. For instance is_call(x, "list", ns = c("", "base")) will match if x is list() or if it’s base::list(): • call_modify() has better support for ... and now treats it like a named argument. call_modify(call, ... = ) adds ... to the call and call_modify(call, ... = NULL) removes it. • call_modify() now preserves empty arguments. It is no longer necessary to use missing_arg() to add a missing argument to a call. This is possible thanks to the new .preserve_empty option of dots_list(). • call_modify() now supports removing unexisting arguments (#393) and passing multiple arguments with the same name (#398). The new .homonyms argument controls how to treat these arguments. • call_standardise() now handles primitive functions like ~ properly (#473). • call_print_type() indicates how a call is deparsed and printed at the console by R: prefix, infix, and special form. • The call_ functions such as call_modify() now correctly check that their input is the right type (#187). ## Other improvements and fixes • New function zap() returns a sentinel that instructs functions like env_bind() or call_modify() that objects are to be removed. • New function rep_named() repeats value along a character vector of names. • New function exec() is a simpler replacement to invoke() (#536). invoke() has been soft-deprecated. • Lambda functions created from formulas with as_function() are now classed. Use is_lambda() to check a function was created with the formula shorthand. • is_integerish() now supports large double values (#578). • are_na() now requires atomic vectors (#558). • The operator %@% has now a replacement version to update attributes of an object (#207). • fn_body() always returns a { block, even if the function has a single expression. For instance fn_body(function(x) do()) returns quote({ do() }). • is_string() now returns FALSE for NA_character_. • The vector predicates have been rewritten in C for performance. • The finite argument of is_integerish() is now NULL by default. Missing values are now considered as non-finite for consistency with base::is.finite(). • is_bare_integerish() and is_scalar_integerish() gain a finite argument for consistency with is_integerish(). • flatten_if() and squash_if() now handle primitive functions like base::is.list() as predicates. • is_symbol() now accepts a character vector of names to mach the symbol against. • parse_exprs() and parse_quos() now support character vectors. Note that the output may be longer than the input as each string may yield multiple expressions (such as "foo; bar"). • parse_quos() now adds the quosures class to its output. ## Lifecycle ### Soft-deprecated functions and arguments rlang 0.3.0 introduces a new warning mechanism for soft-deprecated functions and arguments. A warning is issued, but only under one of these circumstances: • rlang has been attached with a library() call. • The deprecated function has been called from the global environment. In addition, deprecation warnings appear only once per session in order to not be disruptive. Deprecation warnings shouldn’t make R CMD check fail for packages using testthat. However, expect_silent() can transform the warning to a hard failure. #### tidyeval • .data[[foo]] is now an unquote operator. This guarantees that foo is evaluated in the context rather than the data mask and makes it easier to treat .data[["bar"]] the same way as a symbol. For instance, this will help ensuring that group_by(df, .data[["name"]]) and group_by(df, name) produce the same column name. • Automatic naming of expressions now uses a new deparser (still unexported) instead of quo_text(). Following this change, automatic naming is now compatible with all object types (via pillar::type_sum() if available), prevents multi-line names, and ensures name and .data[["name"]] are given the same default name. • Supplying a name with !!! calls is soft-deprecated. This name is ignored because only the names of the spliced vector are applied. • Quosure lists returned by quos() and enquos() now have “list-of” behaviour: the types of new elements are checked when adding objects to the list. Consequently, assigning non-quosure objects to quosure lists is now soft-deprecated. Please coerce to a bare list with as.list() beforehand. • as_quosure() now requires an explicit environment for symbols and calls. This should typically be the environment in which the expression was created. • names() and length() methods for data pronouns are deprecated. It is no longer valid to write names(.data) or length(.data). • Using as.character() on quosures is soft-deprecated (#523). #### Miscellaneous • Using get_env() without supplying an environment is now soft-deprecated. Please use current_env() to retrieve the current environment. • The frame and stack API is soft-deprecated. Some of the functionality has been replaced by trace_back(). • The new_vector_along() family is soft-deprecated because these functions are longer to type than the equivalent rep_along() or rep_named() calls without added clarity. • Passing environment wrappers like formulas or functions to env_ functions is now soft-deprecated. This internal genericity was causing confusion (see issue #427). You should now extract the environment separately before calling these functions. This change concerns env_depth(), env_poke_parent(), env_parent<-, env_tail(), set_env(), env_clone(), env_inherits(), env_bind(), scoped_bindings(), with_bindings(), env_poke(), env_has(), env_get(), env_names(), env_bind_exprs() and env_bind_fns(). • cnd_signal() now always installs a muffling restart for non-critical conditions. Consequently the .mufflable argument has been soft-deprecated and no longer has any effect. ### Deprecated functions and arguments Deprecated functions and arguments issue a warning inconditionally, but only once per session. • Calling UQ() and UQS() with the rlang namespace qualifier is deprecated as of rlang 0.3.0. Just use the unqualified forms instead: # Bad rlang::expr(mean(rlang::UQ(var) * 100)) # Ok rlang::expr(mean(UQ(var) * 100)) # Good rlang::expr(mean(!!var * 100)) Although soft-deprecated since rlang 0.2.0, UQ() and UQS() can still be used for now. • The call argument of abort() and condition constructors is now deprecated in favour of storing full backtraces. • The .standardise argument of call_modify() is deprecated. Please use call_standardise() beforehand. • The sentinel argument of env_tail() has been deprecated and renamed to last. ### Defunct functions and arguments Defunct functions and arguments throw an error when used. • as_dictionary() is now defunct. • The experimental function rst_muffle() is now defunct. Please use cnd_muffle() instead. Unlike its predecessor, cnd_muffle() is not generic. It is marked as a calling handler and thus can be passed directly to with_handlers() to muffle specific conditions (such as specific subclasses of warnings). • cnd_inform(), cnd_warn() and cnd_abort() are retired and defunct. The old cnd_message(), cnd_warning(), cnd_error() and new_cnd() constructors deprecated in rlang 0.2.0 are now defunct. • Modifying a condition with cnd_signal() is defunct. In addition, creating a condition with cnd_signal() is soft-deprecated, please use the new function [signal()] instead. • inplace() has been renamed to calling() to follow base R terminology more closely. ### Functions and arguments in the questioning stage We are no longer convinced these functions are the right approach but we do not have a precise alternative yet. • The functions from the restart API are now in the questioning lifecycle stage. It is not clear yet whether we want to recommend restarts as a style of programming in R. • prepend() and modify() are in the questioning stage, as well as as_logical(), as_character(), etc. We are still figuring out what vector tools belong in rlang. • flatten(), squash() and their atomic variants are now in the questioning lifecycle stage. They have slightly different semantics than the flattening functions in purrr and we are currently rethinking our approach to flattening with the new typing facilities of the vctrs package. # rlang 0.2.2 2018-08-16 This is a maintenance release that fixes several garbage collection protection issues. # rlang 0.2.1 2018-05-30 This is a maintenance release that fixes several tidy evaluation issues. • Functions with tidy dots support now allow splicing atomic vectors. • Quosures no longer capture the current srcref. • Formulas are now evaluated in the correct environment by eval_tidy(). This fixes issues in dplyr and other tidy-evaluation interfaces. # rlang 0.2.0 2018-02-20 This release of rlang is mostly an effort at polishing the tidy evaluation framework. All tidy eval functions and operators have been rewritten in C in order to improve performance. Capture of expression, quasiquotation, and evaluation of quosures are now vastly faster. On the UI side, many of the inconveniences that affected the first release of rlang have been solved: • The !! operator now has the precedence of unary + and - which allows a much more natural syntax: !!a > b only unquotes a rather than the whole a > b expression. • enquo() works in magrittr pipes: mtcars %>% select(!!enquo(var)). • enquos() is a variant of quos() that has a more natural interface for capturing multiple arguments and .... See the first section below for a complete list of changes to the tidy evaluation framework. This release also polishes the rlang API. Many functions have been renamed as we get a better feel for the consistency and clarity of the API. Note that rlang as a whole is still maturing and some functions are even experimental. In order to make things clearer for users of rlang, we have started to develop a set of conventions to document the current stability of each function. You will now find “lifecycle” sections in documentation topics. In addition we have gathered all lifecycle information in the ?rlang::lifecycle help page. Please only use functions marked as stable in your projects unless you are prepared to deal with occasional backward incompatible updates. ## Tidy evaluation • The backend for quos(), exprs(), list2(), dots_list(), etc is now written in C. This greatly improve the performance of dots capture, especially with the splicing operator !!! which now scales much better (you’ll see a 1000x performance gain in some cases). The unquoting algorithm has also been improved which makes enexpr() and enquo() more efficient as well. • The tidy eval !! operator now binds tightly. You no longer have to wrap it in parentheses, i.e. !!x > y will only unquote x. Technically the !! operator has the same precedence as unary - and +. This means that !!a:b and !!a + b are equivalent to (!!a):b and (!!a) + b. On the other hand !!a^b and !!a$b are equivalent to!!(a^b) and !!(a\$b).

• The print method for quosures has been greatly improved. Quosures no longer appear as formulas but as expressions prefixed with ^; quosures are colourised according to their environment; unquoted objects are displayed between angular brackets instead of code (i.e. an unquoted integer vector is shown as <int: 1, 2> rather than 1:2); unquoted S3 objects are displayed using pillar::type_sum() if available.

• New enquos() function to capture arguments. It treats ... the same way as quos() but can also capture named arguments just like enquo(), i.e. one level up. By comparison quos(arg) only captures the name arg rather than the expression supplied to the arg argument.

In addition, enexprs() is like enquos() but like exprs() it returns bare expressions. And ensyms() expects strings or symbols.

• It is now possible to use enquo() within a magrittr pipe:

select_one <- function(df, var) {
df %>% dplyr::select(!!enquo(var))
}

Technically, this is because enquo() now also captures arguments in parents of the current environment rather than just in the current environment. The flip side of this increased flexibility is that if you made a typo in the name of the variable you want to capture, and if an object of that name exists anywhere in the parent contexts, you will capture that object rather than getting an error.

• quo_expr() has been renamed to quo_squash() in order to better reflect that it is a lossy operation that flattens all nested quosures.

• !!! now accepts any kind of objects for consistency. Scalar types are treated as vectors of length 1. Previously only symbolic objects like symbols and calls were treated as such.

• ensym() is a new variant of enexpr() that expects a symbol or a string and always returns a symbol. If a complex expression is supplied it fails with an error.

• exprs() and quos() gain a .unquote_names arguments to switch off interpretation of := as a name operator. This should be useful for programming on the language targetting APIs such as data.table.

• exprs() gains a .named option to auto-label its arguments (#267).

• Functions taking dots by value rather than by expression (e.g. regular functions, not quoting functions) have a more restricted set of unquoting operations. They only support := and !!!, and only at top-level. I.e. dots_list(!!! x) is valid but not dots_list(nested_call(!!! x)) (#217).

• Functions taking dots with list2() or dots_list() now support splicing of NULL values. !!! NULL is equivalent to !!! list() (#242).

• Capture operators now support evaluated arguments. Capturing a forced or evaluated argument is exactly the same as unquoting that argument: the actual object (even if a vector) is inlined in the expression. Capturing a forced argument occurs when you use enquo(), enexpr(), etc too late. It also happens when your quoting function is supplied to lapply() or when you try to quote the first argument of an S3 method (which is necessarily evaluated in order to detect which class to dispatch to). (#295, #300).

• Parentheses around !! are automatically removed. This makes the generated expression call cleaner: (!! sym("name"))(arg). Note that removing the parentheses will never affect the actual precedence within the expression as the parentheses are only useful when parsing code as text. The parentheses will also be added by R when printing code if needed (#296).

• Quasiquotation now supports !! and !!! as functional forms:

expr(!!(var))
quo(call(!!!(var)))

This is consistent with the way native R operators parses to function calls. These new functional forms are to be preferred to UQ() and UQS(). We are now questioning the latter and might deprecate them in a future release.

• The quasiquotation parser now gives meaningful errors in corner cases to help you figure out what is wrong.

• New getters and setters for quosures: quo_get_expr(), quo_get_env(), quo_set_expr(), and quo_set_env(). Compared to get_expr() etc, these accessors only work on quosures and are slightly more efficient.

• quo_is_symbol() and quo_is_call() now take the same set of arguments as is_symbol() and is_call().

• enquo() and enexpr() now deal with default values correctly (#201).

• Splicing a list no longer mutates it (#280).

## Conditions

• The new functions cnd_warn() and cnd_inform() transform conditions to warnings or messages before signalling them.

• cnd_signal() now returns invisibly.

• cnd_signal() and cnd_abort() now accept character vectors to create typed conditions with several S3 subclasses.

• is_condition() is now properly exported.

• Condition signallers such as cnd_signal() and abort() now accept a call depth as call arguments. This allows plucking a call from further up the call stack (#30).

• New helper catch_cnd(). This is a small wrapper around tryCatch() that captures and returns any signalled condition. It returns NULL if none was signalled.

• cnd_abort() now adds the correct S3 classes for error conditions. This fixes error catching, for instance by testthat::expect_error().

## Environments

• env_get_list() retrieves muliple bindings from an environment into a named list.

• with_bindings() and scoped_bindings() establish temporary bindings in an environment.

• is_namespace() is a snake case wrapper around isNamespace().

## Various features

• New functions inherits_any(), inherits_all(), and inherits_only(). They allow testing for inheritance from multiple classes. The _any variant is equivalent to base::inherits() but is more explicit about its behaviour. inherits_all() checks that all classes are present in order and inherits_only() checks that the class vectors are identical.

• New fn_fmls<- and fn_fmls_names<- setters.

• New function experimental function chr_unserialise_unicode() for turning characters serialised to unicode point form (e.g. <U+xxxx>) to UTF-8. In addition, as_utf8_character() now translates those as well. (@krlmlr)

• expr_label() now supports quoted function definition calls (#275).

• call_modify() and call_standardise() gain an argument to specify an environment. The call definition is looked up in that environment when the call to modify or standardise is not wrapped in a quosure.

• is_symbol() gains a name argument to check that that the symbol name matches a string (#287).

• New rlang_box class. Its purpose is similar to the AsIs class from base::I(), i.e. it protects a value temporarily. However it does so by wrapping the value in a scalar list. Use new_box() to create a boxed value, is_box() to test for a boxed value, and unbox() to unbox it. new_box() and is_box() accept optional subclass.

• The vector constructors such as new_integer(), new_double_along() etc gain a names argument. In the case of the _along family it defaults to the names of the input vector.

## Bugfixes

• When nested quosures are evaluated with eval_tidy(), the .env pronoun now correctly refers to the current quosure under evaluation (#174). Previously it would always refer to the environment of the outermost quosure.

• as_pairlist() (part of the experimental API) now supports NULL and objects of type pairlist (#397).

• Fixed a performance bug in set_names() that caused a full copy of the vector names (@jimhester, #366).

## API changes

The rlang API is maturing and still in flux. However we have made an effort to better communicate what parts are stable. We will not introduce breaking changes for stable functions unless the payoff for the change is worth the trouble. See ?rlang::lifecycle for the lifecycle status of exported functions.

• The particle “lang” has been renamed to “call”:

• lang() has been renamed to call2().
• new_language() has ben renamed to new_call().
• is_lang() has been renamed to is_call(). We haven’t replaced the is_unary_lang() and is_binary_lang() because they are redundant with the n argument of is_call().
• All call accessors such as lang_fn(), lang_name(), lang_args() etc are soft-deprecated and renamed with call_ prefix.

In rlang 0.1 calls were called “language” objects in order to follow the R type nomenclature as returned by base::typeof(). We wanted to avoid adding to the confusion between S modes and R types. With hindsight we find it is better to use more meaningful type names.

• We now use the term “data mask” instead of “overscope”. We think data mask is a more natural name in the context of R. We say that that objects from user data mask objects in the current environment. This makes reference to object masking in the search path which is due to the same mechanism (in technical terms, lexical scoping with hierarchically nested environments).

Following this new terminology, the new functions as_data_mask() and new_data_mask() replace as_overscope() and new_overscope(). as_data_mask() has also a more consistent interface. These functions are only meant for developers of tidy evaluation interfaces.

• We no longer require a data mask (previously called overscope) to be cleaned up after evaluation. overscope_clean() is thus soft-deprecated without replacement.

### Breaking changes

• !! now binds tightly in order to match intuitive parsing of tidy eval code, e.g. !! x > y is now equivalent to (!! x) > y. A corollary of this new syntax is that you now have to be explicit when you want to unquote the whole expression on the right of !!. For instance you have to explicitly write !! (x > y) to unquote x > y rather than just x.

• UQ(), UQS() and := now issue an error when called directly. The previous definitions caused surprising results when the operators were invoked in wrong places (i.e. not in quasiquoted arguments).

• The prefix form !!() is now an alias to !! rather than UQE(). This makes it more in line with regular R syntax where operators are parsed as regular calls, e.g. a + b is parsed as +(a, b) and both forms are completely equivalent. Also the prefix form !!!() is now equivalent to !!!.

• UQE() is now deprecated in order to simplify the syntax of quasiquotation. Please use !! get_expr(x) instead.

• expr_interp() now returns a formula instead of a quosure when supplied a formula.

• is_quosureish() and as_quosureish() are deprecated. These functions assumed that quosures are formulas but that is only an implementation detail.

• new_cnd() is now cnd() for consistency with other constructors. Also, cnd_error(), cnd_warning() and cnd_message() are now error_cnd(), warning_cnd() and message_cnd() to follow our naming scheme according to which the type of output is a suffix rather than a prefix.

• is_node() now returns TRUE for calls as well and is_pairlist() does not return TRUE for NULL objects. Use is_node_list() to determine whether an object either of type pairlist or NULL. Note that all these functions are still experimental.

• set_names() no longer automatically splices lists of character vectors as we are moving away from automatic splicing semantics.

### Upcoming breaking changes

• Calling the functional forms of unquote operators with the rlang namespace qualifier is soft-deprecated. UQ() and UQS() are not function calls so it does not make sense to namespace them. Supporting namespace qualifiers complicates the implementation of unquotation and is misleading as to the nature of unquoting (which are syntactic operators at quotation-time rather than function calls at evaluation-time).

• We are now questioning UQ() and UQS() as functional forms of !!. If !! and !!! were native R operators, they would parse to the functional calls !!() and !!!(). This is now the preferred way to unquote with a function call rather than with the operators. We haven’t decided yet whether we will deprecate UQ() and UQS() in the future. In any case we recommend using the new functional forms.

• parse_quosure() and parse_quosures() are soft-deprecated in favour of parse_quo() and parse_quos(). These new names are consistent with the rule that abbreviated suffixes indicate the return type of a function. In addition the new functions require their callers to explicitly supply an environment for the quosures.

• Using f_rhs() and f_env() on quosures is soft-deprecated. The fact that quosures are formulas is an implementation detail that might change in the future. Please use quo_get_expr() and quo_get_env() instead.

• quo_expr() is soft-deprecated in favour of quo_squash(). quo_expr() was a misnomer because it implied that it was a mere expression acccessor for quosures whereas it was really a lossy operation that squashed all nested quosures.

• With the renaming of the lang particle to call, all these functions are soft-deprecated: lang(), is_lang(), lang_fn(), lang_name(), lang_args().

In addition, lang_head() and lang_tail() are soft-deprecated without replacement because these are low level accessors that are rarely needed.

• as_overscope() is soft-deprecated in favour of as_data_mask().

• The node setters were renamed from mut_node_ prefix to node_poke_. This change follows a new naming convention in rlang where mutation is referred to as “poking”.

• splice() is now in questioning stage as it is not needed given the !!! operator works in functions taking dots with dots_list().

• lgl_len(), int_len() etc have been soft-deprecated and renamed with new_ prefix, e.g. new_logical() and new_integer(). This is for consistency with other non-variadic object constructors.

• ll() is now an alias to list2(). This is consistent with the new call2() constructor for calls. list2() and call2() are versions of list() and call() that support splicing of lists with !!!. ll() remains around as a shorthand for users who like its conciseness.

• Automatic splicing of lists in vector constructors (e.g. lgl(), chr(), etc) is now soft-deprecated. Please be explicit with the splicing operator !!!.

# rlang 0.1.6 2017-12-21

• This is a maintenance release in anticipation of a forthcoming change to R’s C API (use MARK_NOT_MUTABLE() instead of SET_NAMED()).

• New function is_reference() to check whether two objects are one and the same.

# rlang 0.1.4 2017-11-05

• eval_tidy() no longer maps over lists but returns them literally. This behaviour is an overlook from past refactorings and was never documented.

# rlang 0.1.2 2017-08-09

This hotfix release makes rlang compatible with the R 3.1 branch.

# rlang 0.1.1 2017-05-18

This release includes two important fixes for tidy evaluation:

• Bare formulas are now evaluated in the correct environment in tidyeval functions.

• enquo() now works properly within compiled functions. Before this release, constants optimised by the bytecode compiler couldn’t be enquoted.

## New functions:

• The new_environment() constructor creates a child of the empty environment and takes an optional named list of data to populate it. Compared to env() and child_env(), it is meant to create environments as data structures rather than as part of a scope hierarchy.

• The new_call() constructor creates calls out of a callable object (a function or an expression) and a pairlist of arguments. It is useful to avoid costly internal coercions between lists and pairlists of arguments.

## UI improvements:

• env_child()’s first argument is now .parent instead of parent.

• mut_ setters like mut_attrs() and environment helpers like env_bind() and env_unbind() now return their (modified) input invisibly. This follows the tidyverse convention that functions called primarily for their side effects should return their input invisibly.

• is_pairlist() now returns TRUE for NULL. We added is_node() to test for actual pairlist nodes. In other words, is_pairlist() tests for the data structure while is_node() tests for the type.

## Bugfixes:

• env() and env_child() can now get arguments whose names start with .. Prior to this fix, these arguments were partial-matching on env_bind()’s .env argument.

• The internal replace_na() symbol was renamed to avoid a collision with an exported function in tidyverse. This solves an issue occurring in old versions of R prior to 3.3.2 (#133).

Initial release.