https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70213
Bug ID: 70213
Summary: Not all ambiguous cases of method constraint
overloading caught?
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xyzdragon at fastmail dot fm
Target Milestone: ---
I'm really a complete novice on the topic of concepts, but I read
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3701.pdf
and on page 5 it introduces constraints for class methods.
#include <iostream>
class A {};
template<class T> bool constexpr isConst() { return false; }
template<> bool constexpr isConst<A>() { return true; }
template<class T>
struct B {
void echo(void) requires isConst<T>()
{ std::cout << "isConst" << std::endl; };
void echo(void) requires isConst<T>() && true
{ std::cout << "isConst && true" << std::endl; };
/*
concepts.cpp:131:13: error: call of overloaded 'echo()' is ambiguous
ba.echo();
=> weirdly the above two functions don't return such ambiguity ...
*/
//void echo(void) requires isConst<T>() && true && true;
void echo(void) requires isConst<T>() && true || false
{ std::cout << "isConst && true || false" << std::endl; };
};
int main( void )
{
B<A> ba;
ba.echo();
return 0;
}
If I don't have a complete brainfreeze at the moment, then (x && true) should
be identical to (x) and (x || false) should be identical to (x). The compiler
doesn't seem to notice that. Furthermore I don't understand why (requires x &&
true) is preferred over (requires x && true || false) and (requires x)
I'm using /opt/gcc-6/bin/g++ --version
g++ (GCC) 6.0.0 20151213 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
