https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81952
Bug ID: 81952
Summary: copy elision used when constructor needs to be called
Product: gcc
Version: 7.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
>From StackOverflow (https://stackoverflow.com/q/45843428/2069064), a reduced
example:
#include <iostream>
template <class T>
struct opt {
opt() { }
opt(opt const& ) { std::cout << "1a\n"; }
opt(opt&& ) { std::cout << "1b\n"; }
template <class U>
opt(U&& ) { std::cout << "2\n"; }
};
struct foo
{
explicit operator opt<int>() { std::cout << "3\n"; return {}; }
};
int main()
{
opt<int> o(foo{});
}
This is direct-initialization of an object not of the same type, so we need to
go through the constructors, the best of which is the template so this program
should print 2. But instead, gcc elides this and just invokes the opt<int>
conversion function and prints 3 (but not 1b, just 3).
