From Jason Turner

[variant.assign]

C++20 → C++23 3.5 KB 22 lines
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Archived: C++20 | C++23
Markdown: C++20 | C++23
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  1. tmp/tmpog4xsqw2/{from.md → to.md} +8 -8
tmp/tmpog4xsqw2/{from.md → to.md} RENAMED
@@ -16,14 +16,14 @@ Let j be `rhs.index()`.
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  - Otherwise, if either `is_nothrow_copy_constructible_v<``Tⱼ``>` is
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  `true` or `is_nothrow_move_constructible_v<``Tⱼ``>` is `false`,
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  equivalent to `emplace<`j`>(get<`j`>(rhs))`.
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  - Otherwise, equivalent to `operator=(variant(rhs))`.
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- *Returns:* `*this`.
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-
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  *Ensures:* `index() == rhs.index()`.
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  *Remarks:* This operator is defined as deleted unless
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  `is_copy_constructible_v<``Tᵢ``> &&` `is_copy_assignable_v<``Tᵢ``>` is
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  `true` for all i. If `is_trivially_copy_constructible_v<``Tᵢ``> &&`
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  `is_trivially_copy_assignable_v<``Tᵢ``> &&`
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  `is_trivially_destructible_v<``Tᵢ``>` is `true` for all i, this
@@ -50,23 +50,23 @@ Let j be `rhs.index()`.
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  *Returns:* `*this`.
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  *Remarks:* If `is_trivially_move_constructible_v<``Tᵢ``> &&`
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  `is_trivially_move_assignable_v<``Tᵢ``> &&`
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  `is_trivially_destructible_v<``Tᵢ``>` is `true` for all i, this
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- assignment operator is trivial. The expression inside `noexcept` is
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- equivalent to:
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  `is_nothrow_move_constructible_v<``Tᵢ``> && is_nothrow_move_assignable_v<``Tᵢ``>`
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  for all i.
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  - If an exception is thrown during the call to `Tⱼ`’s move construction
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  (with j being `rhs.index()`), the `variant` will hold no value.
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  - If an exception is thrown during the call to `Tⱼ`’s move assignment,
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  the state of the contained value is as defined by the exception safety
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  guarantee of `Tⱼ`’s move assignment; `index()` will be j.
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  ``` cpp
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- template<class T> variant& operator=(T&& t) noexcept(see below);
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  ```
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  Let `Tⱼ` be a type that is determined as follows: build an imaginary
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  function *FUN*(Tᵢ) for each alternative type `Tᵢ` for which `Tᵢ`` x[] =`
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  `{std::forward<T>(t)};` is well-formed for some invented variable `x`.
@@ -94,18 +94,18 @@ which is the type of the contained value after assignment.
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  - If `*this` holds a `Tⱼ`, assigns `std::forward<T>(t)` to the value
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  contained in `*this`.
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  - Otherwise, if `is_nothrow_constructible_v<``Tⱼ``, T> ||`
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  `!is_nothrow_move_constructible_v<``Tⱼ``>` is `true`, equivalent to
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  `emplace<`j`>(std::forward<T>(t))`.
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- - Otherwise, equivalent to `operator=(variant(std::forward<T>(t)))`.
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  *Ensures:* `holds_alternative<``Tⱼ``>(*this)` is `true`, with `Tⱼ`
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  selected by the imaginary function overload resolution described above.
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  *Returns:* `*this`.
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- *Remarks:* The expression inside `noexcept` is equivalent to:
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  ``` cpp
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  is_nothrow_assignable_v<Tⱼ&, T> && is_nothrow_constructible_v<Tⱼ, T>
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  ```
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@@ -113,7 +113,7 @@ is_nothrow_assignable_v<Tⱼ&, T> && is_nothrow_constructible_v<Tⱼ, T>
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  `std::forward<T>(t)` to the value contained in `*this`, the state of
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  the contained value and `t` are as defined by the exception safety
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  guarantee of the assignment expression; `valueless_by_exception()`
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  will be `false`.
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  - If an exception is thrown during the initialization of the contained
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- value, the `variant` object might not hold a value.
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  - Otherwise, if either `is_nothrow_copy_constructible_v<``Tⱼ``>` is
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  `true` or `is_nothrow_move_constructible_v<``Tⱼ``>` is `false`,
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  equivalent to `emplace<`j`>(get<`j`>(rhs))`.
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  - Otherwise, equivalent to `operator=(variant(rhs))`.
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  *Ensures:* `index() == rhs.index()`.
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+ *Returns:* `*this`.
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+
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  *Remarks:* This operator is defined as deleted unless
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  `is_copy_constructible_v<``Tᵢ``> &&` `is_copy_assignable_v<``Tᵢ``>` is
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  `true` for all i. If `is_trivially_copy_constructible_v<``Tᵢ``> &&`
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  `is_trivially_copy_assignable_v<``Tᵢ``> &&`
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  `is_trivially_destructible_v<``Tᵢ``>` is `true` for all i, this
 
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  *Returns:* `*this`.
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  *Remarks:* If `is_trivially_move_constructible_v<``Tᵢ``> &&`
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  `is_trivially_move_assignable_v<``Tᵢ``> &&`
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  `is_trivially_destructible_v<``Tᵢ``>` is `true` for all i, this
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+ assignment operator is trivial. The exception specification is
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+ equivalent to
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  `is_nothrow_move_constructible_v<``Tᵢ``> && is_nothrow_move_assignable_v<``Tᵢ``>`
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  for all i.
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  - If an exception is thrown during the call to `Tⱼ`’s move construction
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  (with j being `rhs.index()`), the `variant` will hold no value.
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  - If an exception is thrown during the call to `Tⱼ`’s move assignment,
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  the state of the contained value is as defined by the exception safety
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  guarantee of `Tⱼ`’s move assignment; `index()` will be j.
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  ``` cpp
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+ template<class T> constexpr variant& operator=(T&& t) noexcept(see below);
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  ```
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  Let `Tⱼ` be a type that is determined as follows: build an imaginary
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  function *FUN*(Tᵢ) for each alternative type `Tᵢ` for which `Tᵢ`` x[] =`
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  `{std::forward<T>(t)};` is well-formed for some invented variable `x`.
 
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  - If `*this` holds a `Tⱼ`, assigns `std::forward<T>(t)` to the value
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  contained in `*this`.
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  - Otherwise, if `is_nothrow_constructible_v<``Tⱼ``, T> ||`
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  `!is_nothrow_move_constructible_v<``Tⱼ``>` is `true`, equivalent to
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  `emplace<`j`>(std::forward<T>(t))`.
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+ - Otherwise, equivalent to `emplace<`j`>(``Tⱼ``(std::forward<T>(t)))`.
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  *Ensures:* `holds_alternative<``Tⱼ``>(*this)` is `true`, with `Tⱼ`
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  selected by the imaginary function overload resolution described above.
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  *Returns:* `*this`.
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+ *Remarks:* The exception specification is equivalent to:
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  ``` cpp
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  is_nothrow_assignable_v<Tⱼ&, T> && is_nothrow_constructible_v<Tⱼ, T>
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  ```
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  `std::forward<T>(t)` to the value contained in `*this`, the state of
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  the contained value and `t` are as defined by the exception safety
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  guarantee of the assignment expression; `valueless_by_exception()`
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  will be `false`.
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  - If an exception is thrown during the initialization of the contained
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+ value, the `variant` object is permitted to not hold a value.
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