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Function template transform

hpx::parallel::v1::transform

Synopsis

// In header: <hpx/parallel/container_algorithms/transform.hpp>


template<typename ExPolicy, typename Rng, typename InIter2, typename OutIter, 
         typename F, typename Proj1, typename Proj2, Rng > 
  unspecified transform(ExPolicy && policy, Rng && rng, InIter2 first2, 
                        OutIter dest, F && f, Proj1 && proj1, Proj2 && proj2);

Description

Applies the given function f to pairs of elements from two ranges: one defined by rng and the other beginning at first2, and stores the result in another range, beginning at dest.

[Note] Note

Complexity: Exactly size(rng) applications of f

The invocations of f in the parallel transform algorithm invoked with an execution policy object of type sequential_execution_policy execute in sequential order in the calling thread.

The invocations of f in the parallel transform algorithm invoked with an execution policy object of type parallel_execution_policy or parallel_task_execution_policy are permitted to execute in an unordered fashion in unspecified threads, and indeterminately sequenced within each thread.

Parameters:

dest

Refers to the beginning of the destination range.

f

Specifies the function (or function object) which will be invoked for each of the elements in the sequence specified by [first, last).This is a binary predicate. The signature of this predicate should be equivalent to:

*                      Ret fun(const Type1 &a, const Type2 &b);
*                      


The signature does not need to have const&. The types Type1 and Type2 must be such that objects of types InIter1 and InIter2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. The type Ret must be such that an object of type OutIter can be dereferenced and assigned a value of type Ret.

first2

Refers to the beginning of the second sequence of elements the algorithm will be applied to.

policy

The execution policy to use for the scheduling of the iterations.

proj1

Specifies the function (or function object) which will be invoked for each of the elements of the first sequence as a projection operation before the actual predicate f is invoked.

proj2

Specifies the function (or function object) which will be invoked for each of the elements of the second sequence as a projection operation before the actual predicate f is invoked.

rng

Refers to the sequence of elements the algorithm will be applied to.

Template Parameters:

ExPolicy

The type of the execution policy to use (deduced). It describes the manner in which the execution of the algorithm may be parallelized and the manner in which it executes the invocations of f.

F

The type of the function/function object to use (deduced). Unlike its sequential form, the parallel overload of transform requires F to meet the requirements of CopyConstructible.

InIter2

The type of the source iterators for the second range used (deduced). This iterator type must meet the requirements of an input iterator.

OutIter

The type of the iterator representing the destination range (deduced). This iterator type must meet the requirements of an output iterator.

Proj1

The type of an optional projection function to be used for elements of the first sequence. This defaults to util::projection_identity

Proj2

The type of an optional projection function to be used for elements of the second sequence. This defaults to util::projection_identity

Rng

The type of the source range used (deduced). The iterators extracted from this range type must meet the requirements of an input iterator.

Returns:

The transform algorithm returns a hpx::future<tagged_tuple<tag::in1(InIter1), tag::in2(InIter2), tag::out(OutIter)> > if the execution policy is of type parallel_task_execution_policy and returns tagged_tuple<tag::in1(InIter1), tag::in2(InIter2), tag::out(OutIter)> otherwise. The transform algorithm returns a tuple holding an iterator referring to the first element after the first input sequence, an iterator referring to the first element after the second input sequence, and the output iterator referring to the element in the destination range, one past the last element copied.


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