rlang (version 0.1.6)

dots_list: Extract dots with splicing semantics

Description

These functions evaluate all arguments contained in ... and return them as a list. They both splice their arguments if they qualify for splicing. See ll() for information about splicing and below for the kind of arguments that qualify for splicing.

Usage

dots_list(..., .ignore_empty = c("trailing", "none", "all"))
dots_splice(..., .ignore_empty = c("trailing", "none", "all"))

Arguments

...

Arguments with explicit (dots_list()) or list (dots_splice()) splicing semantics. The contents of spliced arguments are embedded in the returned list.

.ignore_empty

Whether to ignore empty arguments. Can be one of "trailing", "none", "all". If "trailing", only the last argument is ignored if it is empty.

Value

A list of arguments. This list is always named: unnamed arguments are named with the empty string "".

Details

dots_list() has explicit splicing semantics: it splices lists that are explicitly marked for splicing with the splice() adjective. dots_splice() on the other hand has list splicing semantics: in addition to lists marked explicitly for splicing, bare lists are spliced as well.

See Also

exprs() for extracting dots without evaluation.

Examples

# NOT RUN {
# Compared to simply using list(...) to capture dots, dots_list()
# splices explicitly:
x <- list(1, 2)
dots_list(!!! x, 3)

# Unlike dots_splice(), it doesn't splice bare lists:
dots_list(x, 3)

# Splicing is also helpful to workaround exact and partial matching
# of arguments. Let's create a function taking named arguments and
# dots:
fn <- function(data, ...) {
  dots_list(...)
}

# You normally cannot pass an argument named `data` through the dots
# as it will match `fn`'s `data` argument. The splicing syntax
# provides a workaround:
fn(some_data, !!! list(data = letters))

# dots_splice() splices lists marked with splice() as well as bare
# lists:
x <- list(1, 2)
dots_splice(!!! x, 3)
dots_splice(x, 3)
# }