std::transform_exclusive_scan
Defined in header <numeric>


template< class InputIt, class OutputIt, class T, class BinaryOperation, class UnaryOperation> 
(1)  (since C++17) 
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, 
(2)  (since C++17) 
Transforms each element in the range [first, last)
with unary_op
, then computes an exclusive prefix sum operation using binary_op
over the resulting range, with init
as the initial value, and writes the results to the range beginning at d_first
. "exclusive" means that the ith input element is not included in the ith sum.
Formally, assigns through each iterator i
in [d_first, d_first + (last  first)) the value of the generalized noncommutative sum of init, unary_op(*j)...
for every j
in [first, first + (i  d_first)) over binary_op
,
where generalized noncommutative sum GNSUM(op, a
1, ..., a
N) is defined as follows:
 if N=1, a
1  if N > 1, op(GNSUM(op, a
1, ..., a
K), GNSUM(op, a
M, ..., a
N)) for any K where 1 < K+1 = M ≤ N
In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if binary_op
is not associative.
Overload (2) is executed according to policy
, and does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.
unary_op
and binary_op
shall not invalidate iterators (including the end iterators) or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last  first)). Otherwise, the behavior is undefined.
Contents 
[edit] Parameters
first, last    the range of elements to sum 
d_first    the beginning of the destination range, may be equal to first

policy    the execution policy to use. See execution policy for details. 
init    the initial value 
unary_op    unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op .

binary_op    binary FunctionObject that will be applied in to the result of unary_op , the results of other binary_op , and init .

Type requirements  
InputIt must meet the requirements of InputIterator .
 
OutputIt must meet the requirements of OutputIterator .
 
ForwardIt1, ForwardIt2 must meet the requirements of ForwardIterator .
 
T must meet the requirements of MoveConstructible . All of binary_op(init, unary_op(*first)) , binary_op(init, init) , and binary_op(unary_op(*first), unary_op(*first)) must be convertible to T .

[edit] Return value
Iterator to the element past the last element written.
[edit] Complexity
O(last  first) applications of each of binary_op
and unary_op
.
[edit] Exceptions
The overload with a template parameter named ExecutionPolicy
reports errors as follows:
 If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the three standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementationdefined.  If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Notes
unary_op
is not applied to init
.
[edit] Example
This section is incomplete Reason: no example 
[edit] See also
computes the partial sum of a range of elements (function template)  
(C++17) 
similar to std::partial_sum, excludes the ith input element from the ith sum (function template) 
(C++17) 
applies a functor, then calculates inclusive scan (function template) 