On 03/06/2015 01:01 PM, Nicol Bolas wrote:
> The question there is why you need to "syntactically determine if a
> function definition is a template or not"? Why do you care? If the
> compile-time difference is negligible, and you don't need to get a
> function pointer to it, why would you need to know whether it's a
> template or not?

Because this:

   void f(X&& x) {}

may be called with an rvalue or lvalue argument if X is a concept, but
may only be called with an rvalue if X is a type.  That may be important
to a library interface.

And because this:

   void f(X x) {
     static int invoke_count;
     ++invoke_count;
   }

will maintain a count of either every invocation of f() or every
invocation of an instantiation of f() depending on whether X is a
concept or not.

And because this:

   void f(X x) {}

may be moved from a primary source file to a header if X is a concept,
but not if X is a type.

And because this:

   void f(X x) {
       X::type t;
   }

will require 'typename' if X is a concept, but will not allow it if X is
not (of course, the compiler will be happy to tell me about this one).

Why do I care about the above?  Because, in a large code base that I'm
not familiar with, having to go find out what X is detracts from getting
the work done.

Tom.

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