bsl::variant::emplace

Create the alternative with index (template parameter) t_INDEX in place, direct-initialized from the specified il and args', destroying any previously contained value first. Return a reference to the newly created contained value. If the alternative is allocator-aware, it uses the allocator specified upon the construction of this variant object to supply memory; passing an allocator argument to this method results in two allocators being passed to the alternative constructor, resulting in a likely compilation error. If the alternative constructor exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if t_INDEX is a valid alternative index and the designated alternative is constructible from il and args. For simplicity of implementation, this method differs from the standard in the following way: * constexpr is not implemented