Question

If there are 3 interfaces like the following

public interface IWeapon {
void Kill();
}

public interface ISword:IWeapon {
void Slice();
}

public interface IShuriken: IWeapon {
void Pierce();
}

public class Ninja {
public IWeapon Weapon {get;set;}
public void BrutalKill() {

/* warrior must pierce, pierce, pierce and then kill 


*/

}
public void HonorKill {
/* warrior must kill by one slice */
}
}

For a scenario like this how would you wireup the container and what would your method body look like for BrutalKill and HonorKill ?

EDIT: Based on comments, I was thinking on the lines a ninja should be armed with a weapon… if it wants to be armed with a sword or shuriken…should be decided later… not sure if i am thinking right .. maybe we need to subclass Ninja as NinjaWithShuriken and NinjaWithSword

Answer 1

Not sure if this is what you are looking for, but I would have this:

// first some implementations
public class Sword : ISword {
    public void Kill() { // imp }
    public void Slice() { // imp }
}

public class Shuriken : IShuriken {
    public void Kill() { // imp }
    public void Pierce() { // imp }
}

// and I would change the Ninja class to
public class Ninja {
    public ISword Sword { get; private set; }
    public IShuriken Shuriken { get; private set; }

    public Ninja(ISword sword, IShuriken shuriken) {
        this.Sword = sword;
        this.Shuriken = shuriken;
    }

    public void BrutalKill() {
        Shuriken.Pierce();
        Shuriken.Pierce();
        Shuriken.Pierce();

        // either weapon can kill
        // so lets close the distance and use the sword
        Sword.Kill();
    }

    public void HonorKill {
        Sword.Slice();
    }
}

// creating the class
// where Ioc.Resolve is specific to the container implementation
var ninja = new Ninja(IoC.Resolve<ISword>(), IoC.Resolve<IShuriken>());

Update
I like Phil Sandler’s comment so a quick update to reflect that:

// a ninja interface
public interface INinja {
    void BrutalKill();
    void HonorKill();
}

// and then update the ninja class to
public Ninja : INinja {
    ...
}

// and have the ninja class created like this with the container
// resolving the dependencies:
var ninja = IoC.Resolve<INinja>();

Update
Based on the update to the original question I would say:

public interface IWeapon {
    void Attack();
    void Kill();
}

public class Sword : ISword {
    public void Attack() {
        // implement as a slash
    }
    ...
}

public class Shuriken : IShuriken {
    public void Attack() {
        // implement as a pierce
    }
    ...
}

The idea being that we don’t really care how Sword and Shuriken implement Attack, as long as the ninja can use them to perform his duty when called upon. The assassination can be caried out how the specific ninject wishes, as long as the job gets done within the confines of the stated agreement, in this case by Attacking.

// create the specific ninja
var swordNinja = new Ninja(IoC.Resolve<ISword>());
var shurikenNinja = new Ninja(IoC.Resolve<IShuriken>());

// with the ninja class updated to only have an IWeapon 
// property that gets set in the constructor.