apply function {&rest args^+} => {result}{*}
function---a function designator.
args---a spreadable argument list designator.
results---the values returned by function.
Applies the function to the args.
When the function receives its arguments via &rest, it is permissible (but not required) for the implementation to bind the rest parameter to an object that shares structure with the last argument to apply. Because a function can neither detect whether it was called via apply nor whether (if so) the last argument to apply was a constant, conforming programs must neither rely on the list structure of a rest list to be freshly consed, nor modify that list structure.
setf can be used with apply in certain circumstances; see section APPLY Forms as Places.
(setq f '+) => + (apply f '(1 2)) => 3 (setq f #'-) => #<FUNCTION -> (apply f '(1 2)) => -1 (apply #'max 3 5 '(2 7 3)) => 7 (apply 'cons '((+ 2 3) 4)) => ((+ 2 3) . 4) (apply #'+ '()) => 0 (defparameter *some-list* '(a b c)) (defun strange-test (&rest x) (eq x *some-list*)) (apply #'strange-test *some-list*) => implementation-dependent (defun bad-boy (&rest x) (rplacd x 'y)) (bad-boy 'a 'b 'c) has undefined consequences. (apply #'bad-boy *some-list*) has undefined consequences.
(defun foo (size &rest keys &key double &allow-other-keys)
(let ((v (apply #'make-array size :allow-other-keys t keys)))
(if double (concatenate (type-of v) v v) v)))
(foo 4 :initial-contents '(a b c d) :double t)
=> #(A B C D A B C D)
section funcall [Function] , section fdefinition [Accessor] , function, section Evaluation, section APPLY Forms as Places
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