base() and this() constructors best practices

Question

Under what conditions am I supposed to make the :base() and :this() constructor calls following my constructor\'s parentheses (or even in other pl

Answer 1

First off, when they're mandatory.

When a class Derived is derived from a class Base, and Base does not have a default (parameterless) constructor, Derived must call base() explicitly with parameters.

public class Base {
    public Base(int i) { }
}


public class Derived : Base {
    // public Derived() { } wouldn't work - what should be given for i?
    public Derived() : base(7) { }
    public Derived(int i) : base(i) { }
}

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When is it good practice? Whenever you want to call a different constructor.

Suppose you add, in my previous example, content to the constructors in Derived.

public class Derived : Base {
    // public Derived() { } wouldn't work - what should be given for i?
    public Derived() : base(7) {
        Console.WriteLine("The value is " + 7);
    }
    public Derived(int i) : base(i) {
        Console.WriteLine("The value is " + i);
    }
}

You notice the duplication here? It's simpler to call the this() constructor.

public class Derived : Base {
    // public Derived() { } wouldn't work - what should be given for i?
    public Derived() : this(7) { }
    public Derived(int i) : base(i) {
        Console.WriteLine("The value is " + i);
    }
}