cppdraft_translate/cppdraft/variant/helper.md

[variant.helper]

22 General utilities library [utilities]

22.6 Variants [variant]

22.6.4 variant helper classes [variant.helper]

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template<class T> struct variant_size;

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All specializations of variant_size meet theCpp17UnaryTypeTrait requirements ([meta.rqmts]) with a base characteristic of integral_constant<size_t, N> for some N.

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template<class T> struct variant_size<const T>;

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Let VS denote variant_size of the cv-unqualified type T.

Then each specialization of the template meets theCpp17UnaryTypeTrait requirements ([meta.rqmts]) with a base characteristic of integral_constant<size_t, VS​::​value>.

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template<class... Types> struct variant_size<variant<Types...>> : integral_constant<size_t, sizeof...(Types)> { };

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template<size_t I, class T> struct variant_alternative<I, const T>;

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Let VA denote variant_alternative<I, T> of the cv-unqualified type T.

Then each specialization of the template meets the Cpp17TransformationTrait requirements ([meta.rqmts]) with a member typedef type that names the type add_const_t<VA​::​type>.

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variant_alternative<I, variant<Types...>>::type

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Mandates: I < sizeof...(Types).

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Type: The type TI.