Re: [boost] How to detect if f() returns void or not?

Subject: Re: [boost] How to detect if f() returns void or not?
From: Andy Venikov (avenikov_at_[hidden])
Date: 2009-12-15 13:47:06

Eric Niebler wrote:
> 
> Frédéric Bron wrote:
>> I would like to detect if the return type of a function is void or not
>> within C++03 standard?
> <snip>
> 
> I solved this problem once while writing a different trait and 
> documented it here:
> 
> http://www.boost.org/doc/libs/1_41_0/doc/html/proto/appendices.html#boost_proto.appendices.implementation.function_arity 

I gotta admit, this thing is amazing. I actually needed to implement a 
way to tell whether a type is an io manipulator (basically telling if 
calling T(ostream) is a well-formed expression), and was at a loss. I 
was about to post a question on comp.lang.c++ but suddenly came across 
this thread and your solution fit like hand in glove.

I do have a question though.
In your "fununwrap2" class you define the typedef as

typedef private_type const &(*pointer_to_function)
                        (dont_care, dont_care);

and dont_care constructor has ellipsis instead of an argument list.

Why use dont_care at all? Why not define the pointer_to_function type as:

typedef private_type (*pointer_to_function)
                      (...);

It seems to be working just as good.
Or am I missing something?

Thanks,
    Andy.