From Jason Turner

[optional.observe]

C++14 → C++17 2.2 KB 104 lines
Current Draft | LaTeX Source
Archived: C++14 | C++17
Markdown: C++14 | C++17
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  1. tmp/tmp954b21xw/{from.md → to.md} +101 -0
tmp/tmp954b21xw/{from.md → to.md} RENAMED
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+ #### Observers <a id="optional.observe">[[optional.observe]]</a>
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+
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+ ``` cpp
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+ constexpr const T* operator->() const;
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+ constexpr T* operator->();
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+ ```
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+
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+ *Requires:* `*this` contains a value.
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+
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+ *Returns:* `val`.
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+
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+ *Throws:* Nothing.
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+
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+ *Remarks:* These functions shall be constexpr functions.
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+
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+ ``` cpp
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+ constexpr const T& operator*() const&;
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+ constexpr T& operator*() &;
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+ ```
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+
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+ *Requires:* `*this` contains a value.
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+
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+ *Returns:* `*val`.
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+
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+ *Throws:* Nothing.
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+
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+ *Remarks:* These functions shall be constexpr functions.
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+
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+ ``` cpp
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+ constexpr T&& operator*() &&;
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+ constexpr const T&& operator*() const&&;
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+ ```
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+
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+ *Requires:* `*this` contains a value.
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+
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+ *Effects:* Equivalent to: `return std::move(*val);`
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+
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+ ``` cpp
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+ constexpr explicit operator bool() const noexcept;
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+ ```
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+
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+ *Returns:* `true` if and only if `*this` contains a value.
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+
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+ *Remarks:* This function shall be a constexpr function.
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+
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+ ``` cpp
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+ constexpr bool has_value() const noexcept;
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+ ```
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+
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+ *Returns:* `true` if and only if `*this` contains a value.
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+
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+ *Remarks:* This function shall be a constexpr function.
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+
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+ ``` cpp
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+ constexpr const T& value() const&;
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+ constexpr T& value() &;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ return bool(*this) ? *val : throw bad_optional_access();
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+ ```
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+
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+ ``` cpp
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+ constexpr T&& value() &&;
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+ constexpr const T&& value() const&&;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ return bool(*this) ? std::move(*val) : throw bad_optional_access();
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+ ```
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+
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+ ``` cpp
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+ template <class U> constexpr T value_or(U&& v) const&;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ return bool(*this) ? **this : static_cast<T>(std::forward<U>(v));
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+ ```
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+
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+ *Remarks:* If `is_copy_constructible_v<T> && is_convertible_v<U&&, T>`
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+ is `false`, the program is ill-formed.
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+
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+ ``` cpp
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+ template <class U> constexpr T value_or(U&& v) &&;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));
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+ ```
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+
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+ *Remarks:* If `is_move_constructible_v<T> && is_convertible_v<U&&, T>`
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+ is `false`, the program is ill-formed.
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+