BloombergLP::bslstl::Variant_Base::operator=

If the specified rhs holds the same alternative type as this object, move assign the contained value of rhs to the contained value of this object. Otherwise, destroy the currently held alternative object (if any) and, if rhs holds a value, move-construct the corresponding alternative of this object from the contained value of rhs. The allocators of this object and rhs both remain unchanged. If the construction of a new alternative object exits via an exception, this Variant_Base object is left in a valueless by exception state. All alternatives shall be move constructible and move assignable.