Return true if the specified obj currently holds the (template parameter) t_TYPE alternative, and false otherwise. t_TYPE shall appear exactly once in the variant's list of alternatives.
Declared in <bslstl_variant.h>
template<
class t_TYPE,
class t_HEAD,
class... t_TAIL>
bool
holds_alternative(variant<t_HEAD, t_TAIL...> const& obj) noexcept;