C# Language Calling virtual methods in constructor


Example

Unlike C++ in C# you can call a virtual method from class constructor (OK, you can also in C++ but behavior at first is surprising). For example:

abstract class Base
{
    protected Base()
    {
        _obj = CreateAnother();
    }

    protected virtual AnotherBase CreateAnother()
    {
        return new AnotherBase();
    }

    private readonly AnotherBase _obj;
}

sealed class Derived : Base
{
    public Derived() { }

    protected override AnotherBase CreateAnother()
    {
        return new AnotherDerived();
    }
}

var test = new Derived();
// test._obj is AnotherDerived

If you come from a C++ background this is surprising, base class constructor already sees derived class virtual method table!

Be careful: derived class may not been fully initialized yet (its constructor will be executed after base class constructor) and this technique is dangerous (there is also a StyleCop warning for this). Usually this is regarded as bad practice.