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Re: Unbalanced change hooks (part 2) [Documentation fix still remaining]

From: Stefan Monnier
Subject: Re: Unbalanced change hooks (part 2) [Documentation fix still remaining]
Date: Tue, 30 Aug 2016 14:14:51 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux)

>   Normally the before-change-functions and the after-change-functions
>   hooks are called in balanced pairs around each buffer change,

I could agree with that.

>   enabling state to be determined in a before-change function and used in an
>   after-change function.

But this encourages reliance on this pairing, even though experience
shows that it's better to try not to rely on it (both in the sense that
I personally believe that it results in better designs, and in the
sense that such designs will break down in the non-"normal" case).

So I'm strongly opposed to such statements.

>   However on rare occasions, before-change-functions is not called
>   before a buffer change and

That would be documenting bugs as being normal behavior.

>   after-change-functions is thus called twice in succession.  Your
>   program should be ready to deal with such an occurrence.

Two successive calls of a-c-f are indeed acceptable and code should be
ready to deal with such occurrence, but only because a previous b-c-f
call covered both changes, not because b-c-f failed to be called.


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