23 General utilities library [utilities]

23.7 Variants [variant]

23.7.5 Value access [variant.get]

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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....
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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.
4
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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.
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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);
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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.
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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;
7
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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.
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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;
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Requires: The type T occurs exactly once in Types....
Otherwise, the program is ill-formed.
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Effects: Equivalent to: return get_­if<i>(v); with i being the zero-based index of T in Types....