Copy to PRIMARY selection in command

Question

I'm a novice in Lisp, so I feel like I'm missing something very basic here. My intention was to create a function/shortcut to remove all whitespace and newline chars from the selected text and copy the resulting string to the X primary clipboard/selection. For example, when selecting the text:

line 1
line 2

The function should copy line1line2 to the clipboard. To be precise, it should be copied to the primary selection. I've written the following code for this presumably easy task:

(defun copy-no-white-space ()
  (interactive)
  (gui-set-selection
    'PRIMARY
    (replace-regexp-in-string "[\s\n]" "" (buffer-substring (region-beginning) (region-end))))

Unfortunately, this does not work this way. When I try to paste the modified pattern, it only yields the original region with no modifications and I just can not wrap my head around why: It works when PRIMARY is replaced with CLIPBOARD (only that I really want to use PRIMARY). What confuses me even more is the fact that it works with PRIMARY when I remove the regular expression in favor of a fixed string and that it also works when I put it outside of the function. (edit: only when nothing is marked) Why? ;)

Answer 1

After reading Primary Selection I got a clue for the solution. A simple deactivate-mark did the trick for me:

(defun copy-no-white-space ()
  (interactive)
  (deactivate-mark)
  (gui-set-selection
    'PRIMARY
    (replace-regexp-in-string "[\s\n]" "" (buffer-substring (region-beginning) (region-end))))

My interpretation is the following: After leaving the interactive function, X or Emacs(?) re-evaluates the current selection, to bring the highlighted region to the primary clipboard again. Thinking about it, this probably makes a lot sense for other functions that do not actually want to fiddle with the primary selection, I see that my intention is kind of goofy in this sense.