tmp/tmplhsp4axu/{from.md → to.md}
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| 1 |
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### Value access <a id="variant.get">[[variant.get]]</a>
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``` cpp
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template <class T, class... Types>
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constexpr bool holds_alternative(const variant<Types...>& v) noexcept;
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```
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*Requires:* The type `T` occurs exactly once in `Types...`. Otherwise,
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the program is ill-formed.
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*Returns:* `true` if `index()` is equal to the zero-based index of `T`
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in `Types...`.
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``` cpp
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template <size_t I, class... Types>
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constexpr variant_alternative_t<I, variant<Types...>>& get(variant<Types...>& v);
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template <size_t I, class... Types>
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constexpr variant_alternative_t<I, variant<Types...>>&& get(variant<Types...>&& v);
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template <size_t I, class... Types>
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constexpr const variant_alternative_t<I, variant<Types...>>& get(const variant<Types...>& v);
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template <size_t I, class... Types>
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constexpr const variant_alternative_t<I, variant<Types...>>&& get(const variant<Types...>&& v);
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```
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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
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stored in the `variant`. Otherwise, throws an exception of type
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`bad_variant_access`.
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``` cpp
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template <class T, class... Types> constexpr T& get(variant<Types...>& v);
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template <class T, class... Types> constexpr T&& get(variant<Types...>&& v);
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template <class T, class... Types> constexpr const T& get(const variant<Types...>& v);
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template <class T, class... Types> constexpr const T&& get(const variant<Types...>&& v);
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```
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*Requires:* The type `T` occurs exactly once in `Types...`. Otherwise,
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| 39 |
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the program is ill-formed.
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| 40 |
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*Effects:* If `v` holds a value of type `T`, returns a reference to that
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value. Otherwise, throws an exception of type `bad_variant_access`.
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``` cpp
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template <size_t I, class... Types>
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constexpr add_pointer_t<variant_alternative_t<I, variant<Types...>>>
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get_if(variant<Types...>* v) noexcept;
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template <size_t I, class... Types>
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constexpr add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
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get_if(const variant<Types...>* v) noexcept;
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```
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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
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`v != nullptr` and `v->index() == I`. Otherwise, returns `nullptr`.
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``` cpp
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template <class T, class... Types>
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constexpr add_pointer_t<T>
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get_if(variant<Types...>* v) noexcept;
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template <class T, class... Types>
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constexpr add_pointer_t<const T>
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get_if(const variant<Types...>* v) noexcept;
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```
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*Requires:* The type `T` occurs exactly once in `Types...`. Otherwise,
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the program is ill-formed.
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*Effects:* Equivalent to: `return get_if<`i`>(v);` with i being the
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zero-based index of `T` in `Types...`.
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