MinElement.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Algo/Impl/RangePointerType.h"
#include "Templates/IdentityFunctor.h"
#include "Templates/Invoke.h"
#include "Templates/Less.h"
#include "Templates/UnrealTemplate.h" // For MoveTemp
 
namespace AlgoImpl
{
    template <typename RangeType, typename ProjectionType, typename PredicateType>
    typename TRangePointerType<RangeType>::Type MinElementBy(RangeType& Range, ProjectionType Proj, PredicateType Pred)
    {
        typename TRangePointerType<RangeType>::Type Result = nullptr;
 
        for (auto& Elem : Range)
        {
            if (!Result || Invoke(Pred, Invoke(Proj, Elem), Invoke(Proj, *Result)))
            {
                Result = &Elem;
            }
        }
 
        return Result;
    }
}
 
namespace Algo
{
    /**
     * Returns a pointer to the minimum element in a range.
     * If the range contains multiple minimum elements, a pointer to the first one will be returned.
     *
     * @param  Range  The range to find the minimum element in.
     * @return A pointer to the minimum element, or nullptr if the range was empty.
     */
    template <typename RangeType>
    FORCEINLINE auto MinElement(RangeType& Range)
        -> decltype(AlgoImpl::MinElementBy(Range, FIdentityFunctor(), TLess<>()))
    {
        return AlgoImpl::MinElementBy(Range, FIdentityFunctor(), TLess<>());
    }
 
    /**
     * Returns a pointer to the minimum element in a range with a user-defined binary comparator.
     * If the range contains multiple minimum elements, a pointer to the first one will be returned.
     *
     * @param  Range  The range to find the minimum element in.
     * @param  Comp   The comparator to use when comparing two elements.
     * @return A pointer to the minimum element, or nullptr if the range was empty.
     */
    template <typename RangeType, typename ComparatorType>
    FORCEINLINE auto MinElement(RangeType& Range, ComparatorType Comp)
        -> decltype(AlgoImpl::MinElementBy(Range, FIdentityFunctor(), MoveTemp(Comp)))
    {
        return AlgoImpl::MinElementBy(Range, FIdentityFunctor(), MoveTemp(Comp));
    }
 
    /**
     * Returns a pointer to the minimum element in a range with a user-defined binary comparator.
     * If the range contains multiple minimum elements, a pointer to the first one will be returned.
     *
     * @param  Range  The range to find the minimum element in.
     * @param  Proj   The projection to apply to the element to use for comparison.
     * @return A pointer to the minimum element, or nullptr if the range was empty.
     */
    template <typename RangeType, typename ProjectionType>
    FORCEINLINE auto MinElementBy(RangeType& Range, ProjectionType Proj)
        -> decltype(AlgoImpl::MinElementBy(Range, MoveTemp(Proj), TLess<>()))
    {
        return AlgoImpl::MinElementBy(Range, MoveTemp(Proj), TLess<>());
    }
 
    /**
     * Returns a pointer to the minimum element in a range with a user-defined binary comparator.
     * If the range contains multiple minimum elements, a pointer to the first one will be returned.
     *
     * @param  Range  The range to find the minimum element in.
     * @param  Proj   The projection to apply to the element to use for comparison.
     * @param  Comp   The comparator to use when comparing two elements.
     * @return A pointer to the minimum element, or nullptr if the range was empty.
     */
    template <typename RangeType, typename ProjectionType, typename ComparatorType>
    FORCEINLINE auto MinElementBy(RangeType& Range, ProjectionType Proj, ComparatorType Comp)
        -> decltype(AlgoImpl::MinElementBy(Range, MoveTemp(Proj), MoveTemp(Comp)))
    {
        return AlgoImpl::MinElementBy(Range, MoveTemp(Proj), MoveTemp(Comp));
    }
}