From Jason Turner

[futures.unique.future]

C++20 → C++23 2.8 KB 29 lines
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Archived: C++20 | C++23
Markdown: C++20 | C++23
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  1. tmp/tmpepcazdb0/{from.md → to.md} +13 -9
tmp/tmpepcazdb0/{from.md → to.md} RENAMED
@@ -17,13 +17,13 @@ move-assignment operator, `share`, or `valid` on a `future` object for
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  which `valid() == false` is undefined.
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  [*Note 2*: It is valid to move from a future object for which
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  `valid() == false`. — *end note*]
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- [*Note 3*: Implementations should detect this case and throw an object
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- of type `future_error` with an error condition of
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- `future_errc::no_state`. — *end note*]
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  ``` cpp
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  namespace std {
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  template<class R>
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  class future {
@@ -49,10 +49,13 @@ namespace std {
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  future_status wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
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  };
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  }
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  ```
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  The implementation provides the template `future` and two
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  specializations, `future<R&>` and `future<{}void>`. These differ only in
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  the return type and return value of the member function `get`, as set
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  out in its description, below.
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@@ -88,29 +91,30 @@ state that was originally referred to by `rhs` (if any).
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  ``` cpp
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  future& operator=(future&& rhs) noexcept;
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  ```
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- *Effects:*
 
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  - Releases any shared state [[futures.state]].
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  - move assigns the contents of `rhs` to `*this`.
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  *Ensures:*
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  - `valid()` returns the same value as `rhs.valid()` prior to the
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  assignment.
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- - `rhs.valid() == false`.
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  ``` cpp
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  shared_future<R> share() noexcept;
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  ```
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  *Returns:* `shared_future<R>(std::move(*this))`.
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- *Ensures:* `valid() == false`.
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-
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  ``` cpp
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  R future::get();
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  R& future<R&>::get();
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  void future<void>::get();
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  ```
@@ -123,10 +127,12 @@ member function `get`. — *end note*]
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  - `wait()`s until the shared state is ready, then retrieves the value
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  stored in the shared state;
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  - releases any shared state [[futures.state]].
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  *Returns:*
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  - `future::get()` returns the value `v` stored in the object’s shared
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  state as `std::move(v)`.
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  - `future<R&>::get()` returns the reference stored as value in the
@@ -134,12 +140,10 @@ member function `get`. — *end note*]
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  - `future<void>::get()` returns nothing.
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  *Throws:* The stored exception, if an exception was stored in the shared
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  state.
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- *Ensures:* `valid() == false`.
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-
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  ``` cpp
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  bool valid() const noexcept;
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  ```
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  *Returns:* `true` only if `*this` refers to a shared state.
 
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  which `valid() == false` is undefined.
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  [*Note 2*: It is valid to move from a future object for which
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  `valid() == false`. — *end note*]
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+ *Recommended practice:* Implementations should detect this case and
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+ throw an object of type `future_error` with an error condition of
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+ `future_errc::no_state`.
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  ``` cpp
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  namespace std {
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  template<class R>
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  class future {
 
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  future_status wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
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  };
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  }
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  ```
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+ For the primary template, `R` shall be an object type that meets the
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+ *Cpp17Destructible* requirements.
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+
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  The implementation provides the template `future` and two
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  specializations, `future<R&>` and `future<{}void>`. These differ only in
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  the return type and return value of the member function `get`, as set
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  out in its description, below.
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  ``` cpp
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  future& operator=(future&& rhs) noexcept;
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  ```
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+ *Effects:* If `addressof(rhs) == this` is `true`, there are no effects.
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+ Otherwise:
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  - Releases any shared state [[futures.state]].
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  - move assigns the contents of `rhs` to `*this`.
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  *Ensures:*
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  - `valid()` returns the same value as `rhs.valid()` prior to the
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  assignment.
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+ - If `addressof(rhs) == this` is `false`, `rhs.valid() == false`.
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  ``` cpp
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  shared_future<R> share() noexcept;
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  ```
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+ *Ensures:* `valid() == false`.
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+
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  *Returns:* `shared_future<R>(std::move(*this))`.
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  ``` cpp
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  R future::get();
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  R& future<R&>::get();
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  void future<void>::get();
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  ```
 
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  - `wait()`s until the shared state is ready, then retrieves the value
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  stored in the shared state;
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  - releases any shared state [[futures.state]].
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+ *Ensures:* `valid() == false`.
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+
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  *Returns:*
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  - `future::get()` returns the value `v` stored in the object’s shared
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  state as `std::move(v)`.
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  - `future<R&>::get()` returns the reference stored as value in the
 
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  - `future<void>::get()` returns nothing.
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  *Throws:* The stored exception, if an exception was stored in the shared
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  state.
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  ``` cpp
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  bool valid() const noexcept;
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  ```
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  *Returns:* `true` only if `*this` refers to a shared state.