method 'constexpr value_type && expected::value() const &&' does not compile

[marcin-icek]

g++7 setup for c++17
Method of expected class 'constexpr value_type && Expected::value() const &&' does not compile.

In case when You invoke 'value()' method on r-value of 'expected' object the compiler will complain about problem with matching const l-value to r-value, the reason is overloading storage_t::value() method. We have 3 methods value:
1) constexpr value_type const & value() const &
2) value_type & value() &
3) constexpr value_type && value() const &&
In 'expected::value() const &&' we have:
return has_value()
? ( contained.value() ) // contained is a member of expected of type storage_t< T, E >
....
'contained' is l-value and 'expected::value() const &&' is a const method, so the only posible match of overloaded 'storage_t::value()' invoked in 'expected::value() const &&' is (1), which returns value_type const& which cannot be bound to r-value of value_type.