20 General utilities library [utilities]

20.8 Storage for any type [any]

20.8.4 Class any [any.class]

20.8.4.4 Modifiers [any.modifiers]

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template<class T, class... Args> decay_t<T>& emplace(Args&&... args);
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Let VT be decay_­t<T>.
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Constraints: is_­copy_­constructible_­v<VT> is true and is_­constructible_­v<VT, Args...> is true.
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Preconditions: VT meets the Cpp17CopyConstructible requirements.
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Effects: Calls reset().
Then initializes the contained value as if direct-non-list-initializing an object of type VT with the arguments std​::​forward<Args>(args)....
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Postconditions: *this contains a value.
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Returns: A reference to the new contained value.
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Throws: Any exception thrown by the selected constructor of VT.
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Remarks: If an exception is thrown during the call to VT's constructor, *this does not contain a value, and any previously contained value has been destroyed.
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template<class T, class U, class... Args> decay_t<T>& emplace(initializer_list<U> il, Args&&... args);
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Let VT be decay_­t<T>.
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Constraints: is_­copy_­constructible_­v<VT> is true and is_­constructible_­v<VT, initializer_­list<U>&, Args...> is true.
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Preconditions: VT meets the Cpp17CopyConstructible requirements.
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Effects: Calls reset().
Then initializes the contained value as if direct-non-list-initializing an object of type VT with the arguments il, std​::​forward<Args>(args)....
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Postconditions: *this contains a value.
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Returns: A reference to the new contained value.
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Throws: Any exception thrown by the selected constructor of VT.
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Remarks: If an exception is thrown during the call to VT's constructor, *this does not contain a value, and any previously contained value has been destroyed.
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void reset() noexcept;
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Effects: If has_­value() is true, destroys the contained value.
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Postconditions: has_­value() is false.
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void swap(any& rhs) noexcept;
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Effects: Exchanges the states of *this and rhs.