libstdc++-v3/testsuite/20_util/result_of/sfinae_friendly_2.cc

   1 // { dg-options "-std=gnu++11" }
   2 // { dg-do compile }
   3
   4 // Copyright (C) 2012-2013 Free Software Foundation, Inc.
   5 //
   6 // This file is part of the GNU ISO C++ Library.  This library is free
   7 // software; you can redistribute it and/or modify it under the
   8 // terms of the GNU General Public License as published by the
   9 // Free Software Foundation; either version 3, or (at your option)
  10 // any later version.
  11
  12 // This library is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // You should have received a copy of the GNU General Public License along
  18 // with this library; see the file COPYING3.  If not see
  19 // <http://www.gnu.org/licenses/>.
  20
  21 // Taken from N3436:
  22
  23 #include <type_traits>
  24 #include <string>
  25
  26 struct eat { template<typename T> eat(T const &) {} };
  27 struct not_incrementable {};
  28
  29 struct inc {
  30  template<typename T>
  31  auto operator()(T t) const -> decltype(t++)
  32  { return t++; }
  33 };
  34
  35 template<typename A>
  36 typename std::result_of<inc(A)>::type // sfinae here
  37 try_inc(A a) {
  38   return inc()(a);
  39 }
  40
  41 not_incrementable
  42 try_inc(eat) {
  43   return not_incrementable();
  44 }
  45
  46 template<typename>
  47 struct never { static const bool value = false; };
  48
  49 template<typename T>
  50 struct Fail
  51 {
  52   static_assert(never<T>::value, "duh");
  53   typedef int type;
  54 };
  55
  56 struct Fun
  57 {
  58   template<typename T>
  59   typename Fail<T>::type operator()(T)
  60   { return 0; }
  61 };
  62
  63 template<typename T>
  64 typename std::result_of<Fun(T)>::type foo(T)
  65 { return 0; }
  66
  67 template<typename>
  68 int foo(...)
  69 { return 0; }
  70
  71 void result_of_sfinae() {
  72   int x = try_inc(1); // OK
  73   not_incrementable y = try_inc(std::string("foo")); // OK, not_incrementable
  74   (void) x;
  75   (void) y;
  76 }