Re: [Emacs-diffs] trunk r117846: Add macros to allocate temporary Lisp objects with alloca.

[Paul Eggert <eggert@cs.ucla.edu>]

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.