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#' @title Hook to wrap commands
#' @export
#' @family hooks
#' @description Wrap the command of each target in an arbitrary R expression.
#' @details The expression you supply to `hook`
#' must contain the special placeholder symbol `.x`
#' so `tar_hook_outer()` knows where to insert the original command
#' of the target.
#' @return A flattened list of target objects with the hooks applied.
#' Even if the input target list had a nested structure,
#' the return value is a simple list where each element is a target object.
#' All hook functions remove the nested structure of the input target list.
#' @inheritSection tar_map Target objects
#' @inheritParams tar_hook_before
#' @param hook R code to wrap each target's command.
#' The hook must contain the special placeholder symbol `.x`
#' so `tar_hook_outer()` knows where to insert the original command
#' of the target.
#' The hook code is quoted (not evaluated) so there is no need
#' to wrap it in `quote()`, `expression()`, or similar.
#' @examples
#' if (identical(Sys.getenv("TAR_LONG_EXAMPLES"), "true")) {
#' targets::tar_dir({ # tar_dir() runs code from a temporary directory.
#' targets::tar_script({
#' targets <- list(
#' # Nested target lists work with hooks.
#' list(
#' targets::tar_target(x1, task1()),
#' targets::tar_target(x2, task2(x1))
#' ),
#' targets::tar_target(x3, task3(x2)),
#' targets::tar_target(y1, task4(x3))
#' )
#' tarchetypes::tar_hook_outer(
#' targets = targets,
#' hook = postprocess(.x, arg = "value"),
#' names = starts_with("x")
#' )
#' })
#' targets::tar_manifest(fields = command)
#' })
#' }
tar_hook_outer <- function(targets, hook, names = NULL, set_deps = TRUE) {
targets::tar_assert_scalar(set_deps)
targets::tar_assert_lgl(set_deps)
targets::tar_assert_nonmissing(set_deps)
targets <- tar_copy_targets(targets)
hook <- substitute(hook)
targets::tar_assert_lang(hook)
assert_hook_placeholder(hook)
names_quosure <- rlang::enquo(names)
walk_targets(
targets = targets,
names_quosure = names_quosure,
fun = tar_hook_outer_insert,
hook = hook,
set_deps = set_deps
)
targets
}
tar_hook_outer_insert <- function(target, hook, set_deps) {
assert_hook_expr(target)
lang <- target$command$expr[[1]]
expr <- tar_sub_expr(hook, values = list(.x = lang))
tar_replace_command(target = target, expr = expr, set_deps = set_deps)
}
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