25 Algorithms library [algorithms]

25.10 Generalized numeric operations [numeric.ops]

25.10.4 Reduce [reduce]

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template<class InputIterator> constexpr typename iterator_traits<InputIterator>::value_type reduce(InputIterator first, InputIterator last);
1
#
Effects: Equivalent to: return reduce(first, last, typename iterator_traits<InputIterator>::value_type{});
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template<class ExecutionPolicy, class ForwardIterator> typename iterator_traits<ForwardIterator>::value_type reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last);
2
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Effects: Equivalent to: return reduce(std::forward<ExecutionPolicy>(exec), first, last, typename iterator_traits<ForwardIterator>::value_type{});
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template<class InputIterator, class T> constexpr T reduce(InputIterator first, InputIterator last, T init);
3
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Effects: Equivalent to: return reduce(first, last, init, plus<>());
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template<class ExecutionPolicy, class ForwardIterator, class T> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init);
4
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Effects: Equivalent to: return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());
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template<class InputIterator, class T, class BinaryOperation> constexpr T reduce(InputIterator first, InputIterator last, T init, BinaryOperation binary_op); template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init, BinaryOperation binary_op);
5
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Mandates: All of
  • (5.1)
    binary_­op(init, *first),
  • (5.2)
    binary_­op(*first, init),
  • (5.3)
    binary_­op(init, init), and
  • (5.4)
    binary_­op(*first, *first)
are convertible to T.
6
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Preconditions:
  • (6.1)
    T meets the Cpp17MoveConstructible (Table 28) requirements.
  • (6.2)
    binary_­op neither invalidates iterators or subranges, nor modifies elements in the range [first, last].
7
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Returns: GENERALIZED_­SUM(binary_­op, init, *i, ...) for every i in [first, last).
8
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Complexity: applications of binary_­op.
9
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[Note 1:
The difference between reduce and accumulate is that reduce applies binary_­op in an unspecified order, which yields a nondeterministic result for non-associative or non-commutative binary_­op such as floating-point addition.
— end note]