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Re: [Emacs-diffs] master b75fb81 1/4: Extend button.el to take callback

From: Lars Ingebrigtsen
Subject: Re: [Emacs-diffs] master b75fb81 1/4: Extend button.el to take callback data
Date: Fri, 02 Aug 2019 20:46:56 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

"Basil L. Contovounesios" <address@hidden> writes:

>   (defun button-callback-action (button)
>     "Call BUTTON's `button-callback' property."
>     (apply #'funcall (button-get button 'button-callback)))
>   (define-button-type 'rcirc-url
>     'face 'rcirc-url
>     'follow-link t
>     'action #'button-callback-action)
>   (make-text-button start (point)
>                     'type 'rcirc-url
>                     'button-callback (list #'browse-url url))
> (Using define-button-type is optional, but encouraged.)

Button is such a nice and light-weight library (especially compared to
widget).  Having to write these wrapper functions to do these trivial
transforms is the one bad thing in the API.

> Button action functions have until now expected a button as an argument,
> but now they may or may not be given a button, and this is determined by
> the presence or not of a button property.  Why introduce this brittle
> backward incompatibility?

I don't see how it's brittle, and it's not backwards incompatible.

If you add a 'button-data 'foo to your buttons, then you presumably want
your action to get the data.  Otherwise, why would you do it?

> Oh, we seem to be interpreting "naming collision" slightly differently.
> I took it to mean that a client of the button library has used a
> property name for one purpose, which is used for another purpose
> elsewhere.
> But what is happening here is that existing code is written with the
> assumption that button action functions receive a button as argument.
> This assumption now breaks down on buttons with a non-nil button-data
> property.  Why make this unnecessary and backward-incompatible change?

I still don't understand what you mean here.

If somebody writes a new button that has 'button-data, how does that
affect the existing button?  If you write a new button, and say
'button-data, then the 'action you've written takes that data as the
argument, not the button.

There's nobody randomly adding 'button-data to random existing code,

(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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