2010-12-23

emacs delete-selection property

http://groups.google.com/group/gnu.emacs.help/browse_frm/thread/cd99a3244258f58e/8ee411d570ff0ef3

---------- Forwarded message ----------
From: Xah Lee
Date: Dec 22, 6:33 pm
Subject: can a command specify overwrite selection behavior?
To: gnu.emacs.help


On Dec 22, 9:12 am, "Drew Adams" wrote:

> > Drew, what i didn't understand is why the insert-date property makes a
> > distinction on whether a command is called by name or by a keyboard
> > shortcut?

> Ah, good question.  Here's the answer:

> (defun delete-selection-pre-hook ()
>   (when (and delete-selection-mode
>              transient-mark-mode mark-active
>                (not buffer-read-only))
>     (let ((type (and (symbolp this-command)
>                          (get this-command ; <=======
>                           'delete-selection))))

> If you debug this (use `message', not `debug-on-entry'!), you'll see that when
> you use `M-x' the value of `this-command' is `execute-extended-command', not
> `insert-date'.  And `execute-extended-command' does not have a non-nil
> `delete-selection' property.

> `execute-extended-command' is a bit special wrt `this-command' and
> `last-command'.  It DTRT in the end, essentially removing itself from the party,
> but that's only at the end.  While `execute-extended-command' is executing, it
> is the value of `this-command'.

> People sometimes get thrown off by this kind of thing, and similar things wrt
> `M-:' (and `C-x C-e', `C-M-x'...).

> The thing to remember is that `M-x' and `M-:' are themselves keys that are bound
> to commands, and that even though they invoke or evaluate other stuff (and that
> other stuff is what we focus on), that is not the same as just invoking or
> evaluating the other stuff directly.  They add their bit to the mix, and
> sometimes that makes a difference.

> It can help to remember that EVERYTHING in Emacs is a COMMAND.  Or, rather,
> every user interaction is via a command.  Outside Emacs we are not used to
> thinking that way (because outside Emacs it is not true).  But even when you hit
> a letter key such as `g' Emacs invokes a command (by default,
> `self-insert-command').

> Always.  Well no, you can undefine keys: (global-unset-key "a") etc., but as a
> general rule it is true.

> (I know that you know all of this, but I find it's worth reminding myself from
> time to time.  Emacs interaction is all about commands.)

hi Drew. Very useful info i do not know about. Thanks.

 Xah

No comments:

Post a Comment