Box a value

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)

as_box(x, class = NULL)

as_box_if(.x, .p, .class = NULL, ...)


x, .x

An R object.

class, .class

For new_box(), an additional class for the boxed value (in addition to rlang_box). For is_box(), as_box() and as_box_if(), a class (or vector of classes) to be passed to inherits_all().


A predicate function.


Arguments passed to .p.


A boxed value to unbox.

  • box
  • new_box
  • is_box
  • as_box
  • as_box_if
  • unbox
library(rlang) # NOT RUN { boxed <- new_box(letters, "mybox") is_box(boxed) is_box(boxed, "mybox") is_box(boxed, "otherbox") unbox(boxed) # as_box() avoids double-boxing: boxed2 <- as_box(boxed, "mybox") boxed2 unbox(boxed2) # Compare to: boxed_boxed <- new_box(boxed, "mybox") boxed_boxed unbox(unbox(boxed_boxed)) # 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") as_box_if("foo", is_null, "null_box") # }
Documentation reproduced from package rlang, version 0.2.0, License: GPL-3

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