Re: is a typedef necessary?

From:
Marc <marc.glisse@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Mon, 6 Sep 2010 08:17:10 -0700 (PDT)
Message-ID:
<959677e1-03ee-4960-8b7d-322ea70d2ba4@d8g2000yqf.googlegroups.com>
On 6 sep, 16:12, Armen Tsirunyan <lordn3m...@gmail.com> wrote:

Thank you very much, Marc

If you take into account linkage (extern "C" vs extern "C++"), some
things can't be written without a typedef.


for example what?


A function that takes as first argument a C function and as second
argument a C++ function, for instance. (note that few compilers
implement this properly)

struct IncrementFunctorClassWithNoOperatorParentheses
{
   static int f(int n) { return n+1; }
   typedef int(*pf) (int);
   operator pf () { return &f; }

};


   (*operator int ())(int) { return &f; }


This still doesn't work on MSVC9.0
error C2091: function returns function
error C2586: incorrect user-defined conversion syntax : illegal
indirections

works with g++ and Intel,
produces "error: must use a typedef to declare a conversion to 'int (*)
(int)'" with clang.


Who is right? :) I mean, does the standard indirectly imply whether or
not (*operator int ())(int) { return &f; } is supposed to work?


The way I understand it, if there was a valid syntax, that would be
it, but the standard says that a conversion-function-id starts with
the keyword operator, so it can't be legal. Also, it is a gcc
extension.

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