Re: Shift selection using interactive spec

[Juri Linkov <juri@jurta.org>]

> I think that `interactive' codes are much better than symbol properties
> for defining the meaning of a command.
>
> When the `interactive' spec is a Lisp expression, that expression
> can call a suitably provided function to do the job.

According to the documentation, the `interactive' spec tells
`call-interactively' how to read arguments to pass to the function.

There is one exception that is not used to read arguments: if the
string begins with `*' then an error is signaled if the buffer is
read-only.  Since when the buffer is read-only, the command is unable
to operate on the buffer any way, it makes no sense for the user to want
to modify this behavior.

OTOH, shift-selection doesn't tell how to read arguments, It even doesn't
define the meaning of a command.  It specifies the behavior of a separate
optional feature invoked before the command call (in this case to set the
mark before the command call).

Moreover, the user might want to disable this feature for some commands or
enable it for some commands.  Modifying the `interactive' spec of a set of
commands in .emacs would be a big burden for the user.  But changing their
properties in .emacs is very easy as users already do for cua-selection-mode.

-- 
Juri Linkov
http://www.jurta.org/emacs/