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Re: [Emacs-diffs] trunk r117987: * internals.texi (Stack-allocated Objec

From: Stefan Monnier
Subject: Re: [Emacs-diffs] trunk r117987: * internals.texi (Stack-allocated Objects): Describe this feature.
Date: Tue, 30 Sep 2014 16:20:01 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4.50 (gnu/linux)

> For example, we'd have to replace this:
>   caller = concat3 (SCOPED_STRING (" <"), caller, SCOPED_STRING (">"));
> with something like this:
>   SCOPED_STRING (space_lessthan, " <");
>   SCOPED_STRING (greaterthan, ">");
>   caller = concat3 (space_lessthan, caller, greaterthan);

Well, the second looks much better to me.  Its semantics is much clearer.
The extra verbosity helps the programmer think a bit harder about what
she's doing and whether it is really safe to use stack allocation.

> Regardless of whether we use declaration-style macros, there is one thing
> I'd like to change: the macro names.  These macros are not about *scope*;
> they are about *lifetime*.  How about the prefix "auto_" (from the C keyword
> 'auto') rather than "scope_"?  Or maybe "block_" because it's block
> lifetime?  ("auto_" is shorter....)

Maybe it's too obvious, but how 'bout STACK_ALLOC_STRING?
Bikeshedding et al.

> Also, I capitalized SCOPED_STRING on the theory that it is often not
> implemented as a function.  On second thought since it can be (and sometimes
> is) implemented as a function I'm thinking we should make it lower-case, as
> scoped_cons etc. are.  (Correcting its prefix of course.)

That's another advantage of the declaration version: there's no arguing
whether it should be capitalized or not, since it can't be implemented
as a function.


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