From Jason Turner

[optional.ref.ctor]

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tmp/tmpi1f_bvff/{from.md → to.md} RENAMED
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+ #### Constructors <a id="optional.ref.ctor">[[optional.ref.ctor]]</a>
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+
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+ ``` cpp
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+ template<class Arg>
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+ constexpr explicit optional(in_place_t, Arg&& arg);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_constructible_v<T&, Arg>` is `true`, and
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+ - `reference_constructs_from_temporary_v<T&, Arg>` is `false`.
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+
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+ *Effects:* Equivalent to:
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+ *`convert-ref-init-val`*`(std::forward<Arg>(arg))`.
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+
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+ *Ensures:* `*this` contains a value.
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+
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+ ``` cpp
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+ template<class U>
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+ constexpr explicit(!is_convertible_v<U, T&>)
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+ optional(U&& u) noexcept(is_nothrow_constructible_v<T&, U>);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_same_v<remove_cvref_t<U>, optional>` is `false`,
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+ - `is_same_v<remove_cvref_t<U>, in_place_t>` is `false`, and
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+ - `is_constructible_v<T&, U>` is `true`.
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+
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+ *Effects:* Equivalent to:
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+ *`convert-ref-init-val`*`(std::forward<U>(u))`.
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+
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+ *Ensures:* `*this` contains a value.
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+
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+ *Remarks:* This constructor is defined as deleted if
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+
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+ ``` cpp
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+ reference_constructs_from_temporary_v<T&, U>
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+ ```
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+
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+ is `true`.
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+
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+ ``` cpp
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+ template<class U>
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+ constexpr explicit(!is_convertible_v<U&, T&>)
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+ optional(optional<U>& rhs) noexcept(is_nothrow_constructible_v<T&, U&>);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_same_v<remove_cv_t<T>, optional<U>>` is `false`,
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+ - `is_same_v<T&, U>` is `false`, and
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+ - `is_constructible_v<T&, U&>` is `true`.
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ if (rhs.has_value()) convert-ref-init-val(*rhs);
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+ ```
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+
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+ *Remarks:* This constructor is defined as deleted if
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+
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+ ``` cpp
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+ reference_constructs_from_temporary_v<T&, U&>
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+ ```
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+
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+ is `true`.
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+
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+ ``` cpp
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+ template<class U>
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+ constexpr explicit(!is_convertible_v<const U&, T&>)
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+ optional(const optional<U>& rhs) noexcept(is_nothrow_constructible_v<T&, const U&>);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_same_v<remove_cv_t<T>, optional<U>>` is `false`,
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+ - `is_same_v<T&, U>` is `false`, and
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+ - `is_constructible_v<T&, const U&>` is `true`.
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ if (rhs.has_value()) convert-ref-init-val(*rhs);
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+ ```
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+
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+ *Remarks:* This constructor is defined as deleted if
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+
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+ ``` cpp
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+ reference_constructs_from_temporary_v<T&, const U&>
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+ ```
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+
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+ is `true`.
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+
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+ ``` cpp
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+ template<class U>
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+ constexpr explicit(!is_convertible_v<U, T&>)
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+ optional(optional<U>&& rhs) noexcept(is_nothrow_constructible_v<T&, U>);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_same_v<remove_cv_t<T>, optional<U>>` is `false`,
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+ - `is_same_v<T&, U>` is `false`, and
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+ - `is_constructible_v<T&, U>` is `true`.
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ if (rhs.has_value()) convert-ref-init-val(*std::move(rhs));
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+ ```
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+
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+ *Remarks:* This constructor is defined as deleted if
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+
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+ ``` cpp
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+ reference_constructs_from_temporary_v<T&, U>
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+ ```
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+
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+ is `true`.
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+
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+ ``` cpp
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+ template<class U>
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+ constexpr explicit(!is_convertible_v<const U, T&>)
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+ optional(const optional<U>&& rhs) noexcept(is_nothrow_constructible_v<T&, const U>);
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+ ```
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+
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+ *Constraints:*
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+
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+ - `is_same_v<remove_cv_t<T>, optional<U>>` is `false`,
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+ - `is_same_v<T&, U>` is `false`, and
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+ - `is_constructible_v<T&, const U>` is `true`.
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ if (rhs.has_value()) convert-ref-init-val(*std::move(rhs));
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+ ```
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+
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+ *Remarks:* This constructor is defined as deleted if
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+
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+ ``` cpp
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+ reference_constructs_from_temporary_v<T&, const U>
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+ ```
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+
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+ is `true`.
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+