id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
7960	Optimization for move_assign and assign	Antony Polukhin	ebf	"Current implementation of assignment and move assignment creates a `temp` variable if direct_assigner or direct_mover fail. We can avoid it, by checking if the type of variable to assign exactly matches one of the variant types. If it matches, we can do assign without creation of temporary variable.

Here is some pseudo-code to show it:
{{{
    template <typename T>
    void move_assign(T&& rhs)
    {
        // If direct T-to-T move assignment is not possible...
        detail::variant::direct_mover<T> direct_move(rhs);
        if (this->apply_visitor(direct_move) == false)
        {
            if (is_in_varaint_types<T>::value)
            {
                // ... but T is in varaint types, then destroy 
                // content of storage and assign
                move_assigner visitor(*this, type_to_int<T>::value);
                visitor.internal_visit(rhs, 0);
            } 
            else 
            {
                // ...then convert rhs to variant and assign:
                //
                // While potentially inefficient, the following construction of a
                // variant allows T as any type convertible to one of the bounded
                // types without excessive code redundancy.
                //
                variant temp( detail::variant::move(rhs) );
                variant_assign( detail::variant::move(temp) );
            }
        }
    }
}}}"	Feature Requests	closed	To Be Determined	variant	Boost 1.53.0	Optimization	obsolete	variant optimization assignment move