Game logic with C# 7.0 and pattern matching.

c-sharp-pattern-matching.cs

 /**
 * In functional programming, data types do not include operations. Instead, each function implements a single operation
 * for all the data types. This makes it much easier to add a new operation (just define and implement a new function),
 * but much more difficult to add a new data type (modify all existing functions accordingly). While this is already
 * possible in C#, it is much more verbose than it could be.
 */

interface IEnemy
{
    int Health { get; set; }
}

interface IWeapon
{
    int Damage { get; set; }
}
 
class Sword : IWeapon
{
    public int Damage { get; set; }
    public int Durability { get; set; }
}
 
class Bow : IWeapon
{
    public int Damage { get; set; }
    public int Arrows { get; set; }
}
 
static class WeaponOperations
{
    static void Attack(this IWeapon weapon, IEnemy enemy)
    {
        switch (weapon)
        {
            case Sword sword when sword.Durability > 0:
                enemy.Health -= sword.Damage;
                sword.Durability--;
                break;
            case Bow bow when bow.Arrows > 0:
                enemy.Health -= bow.Damage;
                bow.Arrows--;
                break;
        }
    }
 
    static void Repair(this IWeapon weapon)
    {
        if (weapon is Sword)
        {
            var sword = weapon as Sword;
            sword.Durability += 100;
        }
    }
}