`new_box()`

is similar to `base::I()`

but it protects a value by
wrapping it in a scalar list rather than by adding an attribute.
`unbox()`

retrieves the boxed value. `is_box()`

tests whether an
object is boxed with optional class. `as_box()`

ensures that a
value is wrapped in a box. `as_box_if()`

does the same but only if
the value matches a predicate.

new_box(.x, class = NULL, ...) is_box(x, class = NULL) unbox(box)

class | For |
---|---|

... | Additional attributes passed to |

x, .x | An R object. |

box | A boxed value to unbox. |

boxed <- new_box(letters, "mybox") is_box(boxed)#> [1] TRUEis_box(boxed, "mybox")#> [1] TRUEis_box(boxed, "otherbox")#> [1] FALSEunbox(boxed)#> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" #> [20] "t" "u" "v" "w" "x" "y" "z"#> [[1]] #> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" #> [20] "t" "u" "v" "w" "x" "y" "z" #> #> attr(,"class") #> [1] "mybox" "rlang_box"unbox(boxed2)#> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" #> [20] "t" "u" "v" "w" "x" "y" "z"# Compare to: boxed_boxed <- new_box(boxed, "mybox") boxed_boxed#> [[1]] #> [[1]] #> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" #> [20] "t" "u" "v" "w" "x" "y" "z" #> #> attr(,"class") #> [1] "mybox" "rlang_box" #> #> attr(,"class") #> [1] "mybox" "rlang_box"unbox(unbox(boxed_boxed))#> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" #> [20] "t" "u" "v" "w" "x" "y" "z"# Use `as_box_if()` with a predicate if you need to ensure a box # only for a subset of values: as_box_if(NULL, is_null, "null_box")#> [[1]] #> NULL #> #> attr(,"class") #> [1] "null_box" "rlang_box"#> [1] "foo"