23 General utilities library [utilities]
template <class T, class... Types>
constexpr bool holds_alternative(const variant<Types...>& v) noexcept;
Requires:
The type
T occurs exactly once in
Types.... Otherwise, the program is ill-formed
.Returns:
true if
index() is equal to the zero-based index of
T in
Types.... template <size_t I, class... Types>
constexpr variant_alternative_t<I, variant<Types...>>& get(variant<Types...>& v);
template <size_t I, class... Types>
constexpr variant_alternative_t<I, variant<Types...>>&& get(variant<Types...>&& v);
template <size_t I, class... Types>
constexpr const variant_alternative_t<I, variant<Types...>>& get(const variant<Types...>& v);
template <size_t I, class... Types>
constexpr const variant_alternative_t<I, variant<Types...>>&& get(const variant<Types...>&& v);
Requires:
I < sizeof...(Types). Otherwise the program is ill-formed
.Effects:
If
v.index() is
I, returns a reference to the object stored in
the
variant. Otherwise, throws an exception of type
bad_variant_access.template <class T, class... Types> constexpr T& get(variant<Types...>& v);
template <class T, class... Types> constexpr T&& get(variant<Types...>&& v);
template <class T, class... Types> constexpr const T& get(const variant<Types...>& v);
template <class T, class... Types> constexpr const T&& get(const variant<Types...>&& v);
Requires:
The type
T occurs exactly once in
Types.... Otherwise, the program is ill-formed
.Effects:
If
v holds a value of type
T, returns a reference to that value
. Otherwise, throws an exception of type
bad_variant_access.template <size_t I, class... Types>
constexpr add_pointer_t<variant_alternative_t<I, variant<Types...>>>
get_if(variant<Types...>* v) noexcept;
template <size_t I, class... Types>
constexpr add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
get_if(const variant<Types...>* v) noexcept;
Requires:
I < sizeof...(Types). Otherwise the program is ill-formed
.Returns:
A pointer to the value stored in the
variant, if
v != nullptr
and
v->index() == I. Otherwise, returns
nullptr.template <class T, class... Types>
constexpr add_pointer_t<T>
get_if(variant<Types...>* v) noexcept;
template <class T, class... Types>
constexpr add_pointer_t<const T>
get_if(const variant<Types...>* v) noexcept;
Requires:
The type
T occurs exactly once in
Types.... Otherwise, the program is ill-formed
.Effects:
Equivalent to:
return get_if<i>(v); with
i being the zero-based
index of
T in
Types....