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Re: [Emacs-diffs] trunk r117846: Add macros to allocate temporary Lisp o

From: Paul Eggert
Subject: Re: [Emacs-diffs] trunk r117846: Add macros to allocate temporary Lisp objects with alloca.
Date: Tue, 09 Sep 2014 11:37:13 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0

Stefan Monnier wrote:
Any chance `alignas' can be used where we create the stack-allocated
object, maybe?

Although I think we could do that, there would be quite a cost in terms of expressiveness. The macro to create the stack-allocated object would have to expand to a declaration of a local variable, which would mean that it could not be a function-like macro scoped_cons (a, b) but instead would have to be a declaration-like macro SCOPED_NAMED_CONS (name, a, b), where NAME would give the name of the newly-allocated struct Lisp_Cons object.

I'm finding it a bit hard to think about all this, by the way, as it the new definitions aren't used anywhere, which makes it hard to see some of the motivation here.

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