bsl::variant::emplace

Create an object of alternative (template parameter) t_TYPE in place, direct‐initialized from the specified args, destroying any previously contained value first. Return a reference to the newly created t_TYPE object. If t_TYPE 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 constructor of t_TYPE exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if t_TYPE designates a unique alternative and is constructible from args. For simplicity of implementation, this method differs from the standard in the following way: * constexpr is not implemented