From Jason Turner

[reduce]

C++17 → C++20 2.4 KB 34 lines
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Archived: C++17 | C++20
Markdown: C++17 | C++20
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tmp/tmpithzg185/{from.md → to.md} RENAMED
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  ### Reduce <a id="reduce">[[reduce]]</a>
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  ``` cpp
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  template<class InputIterator>
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- typename iterator_traits<InputIterator>::value_type
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  reduce(InputIterator first, InputIterator last);
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  ```
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  *Effects:* Equivalent to:
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@@ -27,11 +27,11 @@ return reduce(std::forward<ExecutionPolicy>(exec), first, last,
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  typename iterator_traits<ForwardIterator>::value_type{});
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  ```
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  ``` cpp
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  template<class InputIterator, class T>
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- T reduce(InputIterator first, InputIterator last, T init);
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
@@ -50,26 +50,33 @@ template<class ExecutionPolicy, class ForwardIterator, class T>
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  return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());
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  ```
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  ``` cpp
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  template<class InputIterator, class T, class BinaryOperation>
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- T reduce(InputIterator first, InputIterator last, T init,
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  BinaryOperation binary_op);
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  template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation>
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  T reduce(ExecutionPolicy&& exec,
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  ForwardIterator first, ForwardIterator last, T init,
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  BinaryOperation binary_op);
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  ```
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- *Requires:*
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-
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- - `T` shall be `MoveConstructible` (Table  [[tab:moveconstructible]]).
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- - All of `binary_op(init, *first)`, `binary_op(*first, init)`,
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- `binary_op(init, init)`, and `binary_op(*first, *first)` shall be
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- convertible to `T`.
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- - `binary_op` shall neither invalidate iterators or subranges, nor
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- modify elements in the range \[`first`, `last`\].
 
 
 
 
 
 
 
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  *Returns:* *GENERALIZED_SUM*(binary_op, init, \*i, ...) for every `i` in
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  \[`first`, `last`).
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  *Complexity:* 𝑂(`last - first`) applications of `binary_op`.
 
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  ### Reduce <a id="reduce">[[reduce]]</a>
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  ``` cpp
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  template<class InputIterator>
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+ constexpr typename iterator_traits<InputIterator>::value_type
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  reduce(InputIterator first, InputIterator last);
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  ```
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  *Effects:* Equivalent to:
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  typename iterator_traits<ForwardIterator>::value_type{});
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  ```
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  ``` cpp
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  template<class InputIterator, class T>
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+ constexpr T reduce(InputIterator first, InputIterator last, T init);
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
 
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  return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());
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  ```
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  ``` cpp
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  template<class InputIterator, class T, class BinaryOperation>
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+ constexpr T reduce(InputIterator first, InputIterator last, T init,
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  BinaryOperation binary_op);
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  template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation>
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  T reduce(ExecutionPolicy&& exec,
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  ForwardIterator first, ForwardIterator last, T init,
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  BinaryOperation binary_op);
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  ```
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+ *Mandates:* All of
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+
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+ - `binary_op(init, *first)`,
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+ - `binary_op(*first, init)`,
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+ - `binary_op(init, init)`, and
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+ - `binary_op(*first, *first)`
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+
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+ are convertible to `T`.
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+
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+ *Preconditions:*
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+
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+ - `T` meets the *Cpp17MoveConstructible* ([[cpp17.moveconstructible]])
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+ requirements.
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+ - `binary_op` neither invalidates iterators or subranges, nor modifies
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+ elements in the range \[`first`, `last`\].
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  *Returns:* *GENERALIZED_SUM*(binary_op, init, \*i, ...) for every `i` in
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  \[`first`, `last`).
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  *Complexity:* 𝑂(`last - first`) applications of `binary_op`.