MRUArray.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Templates/UnrealTypeTraits.h"
#include "Containers/ContainerAllocationPolicies.h"
#include "Containers/Array.h"
 
/*-----------------------------------------------------------------------------
    MRU array.
-----------------------------------------------------------------------------*/
 
template<typename T, typename InAllocator = FDefaultAllocator>
class TMRUArray
    : public TArray<T, InAllocator>
{
public:
    typedef TArray<T, InAllocator> Super;
 
    int32 MaxItems;
 
    [[nodiscard]] TMRUArray()
        : Super()
    {
        MaxItems = 0;
    }
 
    [[nodiscard]] TMRUArray(TMRUArray&&) = default;
    [[nodiscard]] TMRUArray(const TMRUArray&) = default;
    TMRUArray& operator=(TMRUArray&&) = default;
    TMRUArray& operator=(const TMRUArray&) = default;
 
    int32 Add(const T& Item)
    {
        const int32 idx = Super::Add(Item);
        this->Swap(idx, 0);
        CullArray();
        return 0;
    }
 
    int32 AddZeroed(int32 Count = 1)
    {
        const int32 idx = Super::AddZeroed(Count);
        this->Swap(idx, 0);
        CullArray();
        return 0;
    }
 
    int32 AddUnique(const T& Item)
    {
        // Remove any existing copies of the item.
        this->Remove(Item);
        this->Insert(Item, 0);
 
        CullArray();
 
        return 0;
    }
 
    void CullArray()
    {
        // 0 = no limit
        if (!MaxItems)
        {
            return;
        }
 
        while (this->Num() > MaxItems)
        {
            this->RemoveAt(this->Num() - 1, 1);
        }
    }
};