auto-generated move assignment and base or member with a by-value assignment

=?ISO-8859-2?Q?Krzysztof_Czai=F1ski?= <>
Sat, 15 Feb 2014 21:37:40 -0800 (PST)
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If class B has a base or member of type A with an assignment operator
taking A by value, does it implie B's auto-generated move assignment is:
- deleted?
- defaulted?
- not present?

That is, should this sample print "copy" or "move"?

#include <iostream>

struct A
    A() = default;
    A( A const& ) { std::cout << "copy" << std::endl; }
    A( A&& ) { std::cout << "move" << std::endl; }
    A& operator=( A ) { return *this; }

struct B
    A a;

int main()
    B x, y;
    x = std::move(y);

For me it prints "copy" in GCC-4.7, and "move" in MinGW-4.8.

This question originated from [1], where Adam Wulkiewicz tested a
similar sample and from that I expect compilers he used to produce
"copy". Those compilers are:
GCC4.7, Clang3.2, MinGW 4.7, VS2010, VS2013



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