std::swap for non copiable but movable struct - c++

Question

According to C++ reference std::swap is equivalent to
T c(std::move(a)); a=std::move(b); b=std::move(c);
This should allow to swap two non copiable but movable object. Therefore I don't understand why
#include<utility>
struct Foo {
Foo() = delete;
Foo(int) {};
Foo(Foo &) = delete;
Foo(Foo &&) {};
~Foo() {};
};
int main() {
Foo a(1),b(2);
std::swap(a,b);
}
is refused by the compiler with
In file included from /usr/include/c++/4.8/bits/stl_pair.h:59:0,
from /usr/include/c++/4.8/utility:70,
from swap.cpp:1:
/usr/include/c++/4.8/bits/move.h: In instantiation of ‘void std::swap(_Tp&, _Tp&) [with _Tp = Foo]’:
swap.cpp:13:16: required from here
/usr/include/c++/4.8/bits/move.h:176:11: error: use of deleted function ‘Foo& Foo::operator=(const Foo&)’
__a = _GLIBCXX_MOVE(__b);
^
swap.cpp:3:8: note: ‘Foo& Foo::operator=(const Foo&)’ is implicitly declared as deleted because ‘Foo’ declares a move constructor or move assignment operator
struct Foo {
^
In file included from /usr/include/c++/4.8/bits/stl_pair.h:59:0,
from /usr/include/c++/4.8/utility:70,
from swap.cpp:1:
/usr/include/c++/4.8/bits/move.h:177:11: error: use of deleted function ‘Foo& Foo::operator=(const Foo&)’
__b = _GLIBCXX_MOVE(__tmp);
note: this is with GCC 4.8 and 4.9 but clang complain as well.

Answer 1

You declared a move constructor. However, you need a move assignment operator for std::swap. You should add the following two operators:
auto operator=(const Foo& rhs) & -> Foo& = delete;
auto operator=(Foo&& rhs) & noexcept -> Foo&
{
// ...
return *this;
}