unused attribute issue in C++ templates?

[Paul Smith]

Sorry, to be clear I'm using "g++" in all compilations, I'm not using
"gcc" at all.

On Wed, 2013-09-11 at 17:40 -0400, Paul Smith wrote:
> Hi all.  I'm using GCC 4.8.1 that I built myself on Intel (GNU/Linux).
> I'm seeing a strange behavior dealing with __attribute__((unused)) in a
> C++ template.
> 
> I have a macro UNUSED set to that value, and I've been using it (where
> needed, typically when I need to save the value only for use in assert()
> calls) as part of the type of a variable, like this:
> 
>     FooBar* UNUSED foo = something;
>     assert(foo);
> 
> This is working fine, _except_ (apparently) in variables declared in
> methods of a template class (weird!).  In those situations the UNUSED
> seems to be ignored if I write it like that.  By "ignored" I mean that
> in this form, gcc -O3 -D_NDEBUG will generate a warning that the
> variable is not used.
> 
> However if I change it to this:
> 
>     FooBar* foo UNUSED = something;
> 
> then it works (as in, g++ does not generate this warning any longer).
> 
> 
> Anyone have any thoughts about this?  I can try to reduce this to a
> repro case if there's interest.  Or, am I just doing something wrong?
>