Thegeneralized noncommutative sum of a sequence of elements over a binary operationbinary_op is defined as follows:

• If the sequence only has one element, the sum is the value of the element.
• Otherwise, performs the following operations in order:

1. Selects any two adjacent elementselem1 andelem2 from the sequence.
2. Calculatesbinary_op(elem1, elem2) and replaces the two elements in the sequence with the result.
3. Repeats steps 1 and 2 until there is only one element in the sequence.

The result is non-deterministic if thebinary_op is not associative (such as floating-point addition).

For overloads(1,2), ifbinary_op(unary_op(*first), unary_op(*first)) is not convertible to thevalue type ofdecltype(first), the program is ill-formed.

For overloads(3,4), if any of the following values is not convertible toT, the program is ill-formed:

• binary_op(init, init)
• binary_op(init, unary_op(*first))
• binary_op(unary_op(*first), unary_op(*first))

If any of the following conditions is satisfied, the behavior is undefined:

• For overloads(1,2), the value type ofdecltype(first) is notMoveConstructible.
• For overloads(3,4),T is notMoveConstructible.
• unary_op orbinary_op modifies any element of[first, last).
• unary_op orbinary_op invalidates any iterator or subrange of[first, last].

[edit]Parameters

[edit]Return value

Iterator to the element past the last element written.

[edit]Complexity

Given\(\scriptsize N\)N asstd::distance(first, last):

[edit]Exceptions

The overloads with a template parameter namedExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory,std::bad_alloc is thrown.

[edit]Notes

unary_op is never applied toinit.

The parameterinit appears last, differing fromstd::transform_exclusive_scan, because it is optional for this function.

[edit]Example

#include <functional>#include <iostream>#include <iterator>#include <numeric>#include <vector> int main(){std::vector data{3,1,4,1,5,9,2,6}; auto times_10=[](int x){return x*10;}; std::cout<<"10 times exclusive sum: ";std::transform_exclusive_scan(data.begin(), data.end(),std::ostream_iterator<int>(std::cout," "),0,std::plus<int>{}, times_10);std::cout<<"\n10 times inclusive sum: ";    std::transform_inclusive_scan(data.begin(), data.end(),std::ostream_iterator<int>(std::cout," "),std::plus<int>{}, times_10);std::cout<<'\n';}

10 times exclusive sum: 0 30 40 80 90 140 230 250 10 times inclusive sum: 30 40 80 90 140 230 250 310

[edit]See also

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