SlotItemHandlerImmutable.java

package net.neoforged.neoforge.items;

import net.minecraft.world.item.ItemStack;
import org.jetbrains.annotations.Nullable;

public class SlotItemHandlerImmutable extends SlotItemHandler {
    // Vanilla MC code modifies the stack returned by `getItem()` directly, but it
    // calls `setChanged()` when that happens, so we just cache the returned stack,
    // and set it when `setChanged()` is called.
    @Nullable
    private ItemStack cachedReturnedStack = null;

    public SlotItemHandlerImmutable(IItemHandler itemHandler, int index, int xPosition, int yPosition) {
        super(itemHandler, index, xPosition, yPosition);
    }

    @Override
    public ItemStack getItem() {
        return cachedReturnedStack = super.getItem();
    }

    @Override
    public final void set(ItemStack stack) {
        super.set(stack);
        cachedReturnedStack = stack;
    }

    @Override
    public final void setChanged() {
        if (cachedReturnedStack != null) {
            set(cachedReturnedStack);
        }
    }

    @Override
    public final ItemStack remove(int amount) {
        ItemStack stack = getItem().copy();
        ItemStack ret = stack.split(amount);
        set(stack);
        cachedReturnedStack = null;
        return ret;
    }
}