Adding Completion to (interactive)

Author: Tubo

Question:

Is there any way to add my own completion to an (interactive) elisp function? Ideally, I'd
like to pass it a list of strings that it would tab-complete from. I know that using (interactive "D"), (interactive "F") or (interactive "b") give you completion for directories, files and buffer-names respectively, but what about more general inputs?

Answer:

The argument to interactive need not be a string; if it isn't, it's evaluated to get the list of arguments to pass to the function. Therefore, you can do something like this:

(defun insert-foo-bar-or-baz (arg)
  (interactive
   (list
    (completing-read "Choose one: " '("foo" "bar" "baz"))))
  (insert arg))

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