Operator "~", decltype() and templates.

Paweł Tomulik ptomulik@meil.pw.edu.pl
Tue Feb 17 15:10:00 GMT 2015


Hi,

the following program does not compile with g++4.9.2:

#include <iostream>


template<typename T>
auto tt(T x) -> decltype(~x) // <-- here
{ return ~x; }

int main()
{
  std::cout << tt(10) << std::endl;
  return EXIT_SUCCESS;
}

ptomulik@tea:$ g++ -std=c++11 -g -O0 -Wall -Wextra -Werror -pedantic -o
test-gcc test.cpp
test.cpp: In function ‘int main()’:
test.cpp:10:21: error: no matching function for call to ‘tt(int)’
   std::cout << tt(10) << std::endl;
                     ^
test.cpp:10:21: note: candidate is:
test.cpp:5:6: note: template<class T> decltype (~ x) tt(T)
 auto tt(T x) -> decltype(~x)
      ^
test.cpp:5:6: note:   template argument deduction/substitution failed:
test.cpp: In substitution of ‘template<class T> decltype (~ x) tt(T)
[with T = int]’:
test.cpp:10:21:   required from here
test.cpp:5:6: error: ‘x’ was not declared in this scope


This is specific to operator "~". Note, that, for example, any of the
following functions compile without a problem:


template<typename T>
auto tt(T x) -> decltype(-x)
{ return -x; }

template<typename T>
auto tt(T x) -> decltype(!x)
{ return !x; }

template<typename T>
auto tt(T x) -> decltype(+x)
{ return +x; }

template<typename T>
auto tt(T x) -> decltype(~T())
{ return ~x; }


Is this a bug? The original program compiles with clang.

Best Regards!
-- 
Pawel Tomulik



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