inject() evaluates an expression with injection
support. There are three main usages:
Splicing lists of arguments in a function call.
Inline objects or other expressions in an expression with
!!and!!!. For instance to create functions or formulas programmatically.Pass arguments to NSE functions that defuse their arguments without injection support (see for instance
enquo0()). You can use{{ arg }}with functions documented to support quosures. Otherwise, use!!enexpr(arg).
Usage
inject(expr, env = caller_env())Arguments
- expr
An argument to evaluate. This argument is immediately evaluated in
env(the current environment by default) with injected objects and expressions.- env
The environment in which to evaluate
expr. Defaults to the current environment. For expert use only.
Examples
# inject() simply evaluates its argument with injection
# support. These expressions are equivalent:
2 * 3
#> [1] 6
inject(2 * 3)
#> [1] 6
inject(!!2 * !!3)
#> [1] 6
# Injection with `!!` can be useful to insert objects or
# expressions within other expressions, like formulas:
lhs <- sym("foo")
rhs <- sym("bar")
inject(!!lhs ~ !!rhs + 10)
#> foo ~ bar + 10
#> <environment: 0x562ec1e37f50>
# Injection with `!!!` splices lists of arguments in function
# calls:
args <- list(na.rm = TRUE, finite = 0.2)
inject(mean(1:10, !!!args))
#> [1] 5.5