inventory.java

// simply a marker
interface Carrier {
  
  Inventory getInventory();
  
}

interface Inventory {
  
  Collection<ItemStack> getItems();

}

interface ItemList extends Inventory, List<ItemStack> {
}

interface ItemGrid extends Inventory, Map<Integer, ItemStack> {

  ItemStack get(Vector2i pos);
  void set(Vector2i pos, ItemStack stack)

}

// simple getter/setter, no fluff
interface ItemSlot extends Inventory {
  
  ItemStack get();
  void set(ItemStack newItem);
  ItemStack split(int count);
  
}

interface View<I, O> {
  
  List<O> get(I input);

  List<O> get(List<I> input);
  
  <P> View<I, P> andThen(View<O, P> that);

}

interface InventoryView<O> extends View<Inventory, O> { }

interface ViewFuel extends InventoryView<ItemSlot> { }

interface ViewCraftingInput extends InventoryView<Inventory> {}

interface ViewResult extends InventoryView<ItemSlot> {}

interface ViewMatrix extends InventoryView<ItemGrid> {}

class MyPlugin {
  
  @Inject ViewFuel fuel;
  // or
  ViewCraftingInput crafting = Views.of(ViewCraftingInput.class);

  ViewMatrix matrix = Views.of(ViewMatrix.class);

  InventoryView<ItemGrid> comp = crafting.andThen(matrix);
  
  {
    Inventory myInventory = myCarrier.getInventory();
    List<ItemGrid> invfuel = comp.get(myInventory);
  }
  
}