Re: SFINAE with invalid function-type or array-type parameters?

From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 5 May 2009 14:51:04 CST

Message-ID:

<7c6d3bee-e45a-417c-8041-d207d70be281@s20g2000vbp.googlegroups.com>

On 4 Mai, 21:07, litb <Schaub-Johan...@web.de> wrote:

template<typename T>
char (&f(T[1]))[1];

template<typename T>
char (&f(...))[2];

int main() { char c[sizeof(f<void()>(0)) == 2]; }
// snap

I expected it doing SFINAE and chosing the second overload, since
substitution of T into T[1] yields

void [1]()

Which is an invalid type, of course.

My initial thought was that this should work as a function's parameter
type because

  void foo(int x[1]);

is no different from

  void foo(int* x);

By that logic void x[1]() would be equivalent to void(*x)() in this
context. But I could not compile the following snippet

  void foo(void x[1]());

using G++ 4.3.2. It says: "error: declaration of 'x' as array of
functions". Strangely enough it works as a template

  template<typename T>
  void foo(T x[1]) {}

  int main() {
    foo<void()>(0); // compiles fine
  }

Cheers!
SG

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