Cast an object to child type? (Downcasting)

Question

I understand that downcasting may not be the best way to achieve my desires, but it at least indicates the kind of solutions I have running through my head. Any alternative suggestions are welcome.

Alright, so may as well dive into my code:

public void triggerItem(Item item) 
{
    if (item is Weapon) {
        equipWeapon(item);
    }       
}

public void equipWeapon(Weapon weapon) 
{

}

So I basically have an inventory set up, and of course the inventory will contain various types of items (weapons, armour, consumables, etc.) As you can see I have an Item class and then a Weapon class and a bunch of others which all inherit Item.

Now, I intend to call this function when the player clicks on an item in their inventory, then call different functions depending on the particular Type of Item.

But because equipWeapon() receives Weapon, it doesn't like it when I just pass it an Item.

I understand that I could change my code to equipWeapon(Item item), but the ultimate destination of the object requires a Weapon type and I'm reluctant to change that. It seems like a dirty solution and a step in the wrong direction, but feel free to correct me if I'm wrong.

Answer 1

Give your base class a method that causes it to be equipped, and implement it in the type-specific class that knows how to equip itself.

Example:

abstract class Item
{
    public abstract void Equip();
}

class Weapon
{
    public override void Equip()
    {
        equipWeapon(this);
    }
}

Then triggerItem becomes trivial:

public void triggerItem(Item item) 
{
    item.Equip();
}       

If you need to call equipWeapon on a different class (e.g. whatever class contains triggerItem) you can make the class part of the interface:

abstract class Item
{
    public abstract void Equip(Game context);
}

class Weapon
{
    public override void Equip(Game context)
    {
        context.equipWeapon(this);
    }
}

class Game
{
    public void triggerItem(Item item) 
    {
        item.Equip(this);
    }       
}