Question

public Butler(IWeapon weapon): this(weapon, new Communicate())
{}

What does this(weapon, new Communicate()) mean?

Answer 1

It calls another constructor on the same type, passing in the weapon that was passed to this constructor, and a new Communicate object. I assume there is also something like:

// might actually be private
public Butler(IWeapon weapon, Communicate communicate) {...}

This approach is useful by allowing you to have multiple constructors, but only put the code in the most complex one. All the other constructors just pass the arguments (or defaults, as necessary) to the chosen constructor.

The chained constructor gets invoked before the body of the constructor that has the : this(...)