Extended equality operator for std::optional.

gistfile1.cpp

// TODO: Probably necessary to wrap U in decay.

template< class T, class U >
constexpr typename std::enable_if<!std::is_base_of<std::optional<T>, std::optional<U>>::value, bool>::type
operator==( const std::optional<T>& opt, U&& value ) {
	return opt == static_cast<const U&>( value );
}

template< class T, class U >
constexpr typename std::enable_if<!std::is_base_of<std::optional<T>, std::optional<U>>::value, bool>::type
operator==( U&& value, const std::optional<T>& opt ) {
	return static_cast<const U&>( value ) == opt;
}


template< class T, class U >
constexpr typename std::enable_if<!std::is_base_of<std::optional<T>, std::optional<U>>::value, bool>::type
operator!=( const std::optional<T>& opt, U&& value ) {
	return !( opt == value );
}

template< class T, class U >
constexpr typename std::enable_if<!std::is_base_of<std::optional<T>, std::optional<U>>::value, bool>::type
operator!=( U&& value, const std::optional<T>& opt ) {
	return !( opt == value );
}