Transform.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Templates/Invoke.h"
 
/*
 * Inspired by std::transform.
 *
 * Simple example:
 *  TArray<FString> Out;
 *  TArray<int32> Inputs { 1, 2, 3, 4, 5, 6 };
 *  Algo::Transform(
 *      Inputs,
 *      Out,
 *      [](int32 Input) { return LexToString(Input); }
 *  );
 *  // Out1 == [ "1", "2", "3", "4", "5", "6" ]
 *
 * You can also use Transform to output to multiple targets that have an Add function, by using :
 * 
 *  TArray<FString> Out1;
 *  TArray<int32> Out2;
 *
 *  TArray<int32> Inputs = { 1, 2, 3, 4, 5, 6 };
 *  Algo::Transform(
 *      Inputs,
 *      TiedTupleAdd(Out1, Out2),
 *      [](int32 Input) { return ForwardAsTuple(LexToString(Input), Input * Input); }
 *  );
 *
 *  // Out1 == [ "1", "2", "3", "4", "5", "6" ]
 *  // Out2 == [ 1, 4, 9, 16, 25, 36 ]
 */
namespace Algo
{
    /**
     * Conditionally applies a transform to a range and stores the results into a container
     *
     * @param  Input      Any iterable type
     * @param  Output     Container to hold the output
     * @param  Predicate  Condition which returns true for elements that should be transformed and false for elements that should be skipped
     * @param  Trans      Transformation operation
     */
    template <typename InT, typename OutT, typename PredicateT, typename TransformT>
    FORCEINLINE void TransformIf(const InT& Input, OutT&& Output, PredicateT Predicate, TransformT Trans)
    {
        for (const auto& Value : Input)
        {
            if (Invoke(Predicate, Value))
            {
                Output.Add(Invoke(Trans, Value));
            }
        }
    }
 
    /**
     * Applies a transform to a range and stores the results into a container
     *
     * @param  Input   Any iterable type
     * @param  Output  Container to hold the output
     * @param  Trans   Transformation operation
     */
    template <typename InT, typename OutT, typename TransformT>
    FORCEINLINE void Transform(const InT& Input, OutT&& Output, TransformT Trans)
    {
        for (const auto& Value : Input)
        {
            Output.Add(Invoke(Trans, Value));
        }
    }
}