Subject: Re: bug#7381: 24.0.50; Provide a hook run when a window is selected

From: Štěpán Němec <[email-masked]>
Date: Fri, 12 Nov 2010 18:09:36 +0100

martin rudalics <[email-masked]> writes:

>>> Can't you use `window-configuration-change-hook'?
>>
>> I don't see how that would help, as the hook is not run when a window is
>> selected.
>
> Well, we _could_ run it when another window gets selected.  But at the
> time we'd run it the identity of the old selected window would not be
> available anywhere. [...]

Right, but I don't consider that too much of a problem -- I could always
save the last two windows instead of just the last one, for instance.

But I really don't think extending `w-c-c-hook' is the right
solution. I don't see why just selecting another window should be
considered a window configuration change... 

> Basically, we could keep the old window configuration around from one
> "change" to the next but it's not clear whether we want to save the
> configuration before the last command or before the last configuration
> change.  In the latter case, your code would hardly know whether it runs
> within one and the same command or within different commands.
>
> Note in this context that a single command like setting up a GDB frame
> may entail a couple of configuration changes and you would have to keep
> track of all of them.  And the hook would trigger within each and every
> instance of `with-selected-window' or `save-window-excursion' no matter
> how silly these macros are occasionally used.

...and these caveats seem only to confirm such doubts (although some of
them would apply to lesser extent to the hypothetical
`select-window'-specific hook as well).

What's wrong with a separate `window-selected-hook' or perhaps
`select-window-hook'?

[On a related note, it would be nice if there were some clean and simple
way to define custom hooks attached to arbitrary functions; that would
solve problems similar to this one, preventing discussions whether adding
yet another hook is worth it or not. Something like:

  (define-function-hook 'select-window)
  => select-window-hook

  (add-hook 'select-window-hook ...)

Dream on...]

  Štěpán