23 General utilities library [utilities]

23.7 Variants [variant]

23.7.5 Value access [variant.get]

template <class T, class... Types> constexpr bool holds_alternative(const variant<Types...>& v) noexcept;

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Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed.

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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);

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Requires: I < sizeof...(Types). Otherwise the program is ill-formed.

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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);

5
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Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed.

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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;

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Requires: I < sizeof...(Types). Otherwise the program is ill-formed.

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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;

9
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Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed.

10
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Effects: Equivalent to: return get_­if<i>(v); with i being the zero-based index of T in Types....