How do I use :base() and :this() correctly?

Question

I've already searched about this issue both on SO and other websites but I haven't managed to find (or come to) a solution for my case.

I have an abstract class called EnteBase, which I use as a base (duh!) for other two classes, Regione and Provincia.

EnteBase:

public abstract class EnteBase
{
    public EnteBase ()
        : this( "Sconosciuto", 0 )
    {
    }

    public EnteBase ( string nome )
        : this( nome, 0 )
    {
    }

    public EnteBase ( string nome, int numeroComuni )
    {
        this.Nome = nome;
        this.NumeroComuni = numeroComuni;
    }


    private string nome;
    public string Nome
    {
        [...]
    }

    private int numeroComuni;
    public int NumeroComuni
    {
        [...]
    }
}

Regione:

public class Regione : EnteBase
{
    public List<Provincia> Province
    {
        [...]
    }


    public Regione ()
        : base()
    {
        this.Province = new List<Provincia>();
    }

    public Regione ( string nome )
        : this()
    {
    }

    public Regione ( string nome, int numeroComuni )
        : this()
    {
    }


    public void AggiungiProvincia ( Provincia provincia )
    {
        Province.Add( provincia );
    }
}

Provincia:

public class Provincia : EnteBase
{
    private string sigla;

    public string Sigla
    {
        [...]
    }

    public Provincia ()
        : base()
    {
    }

    public Provincia ( string nome )
        : this()
    {
        this.Nome = nome;
    }

    public Provincia ( string nome, int numeroComuni )
        : this()
    {
        this.Nome = nome;
        this.NumeroComuni = numeroComuni;
    }

    public Provincia( string nome, int numeroComuni, string sigla)
        : this()
    {
        this.Nome = nome;
        this.NumeroComuni = numeroComuni;
        this.Sigla = sigla;
    }
}

My questions are the following:

Is it correct to use :this() in all constructors of the base class except the one with most parameters, with the others pointing towards the latter?
Is it correct to use :this() pointing to the base constructor in the classes Provincia and Regione and then assign to the fields from inside the method itself?

My problem rooted from the fact that I wanted to use both :this() and :base() in every method. When I discovered that it was not possible I looked for a solution, but I couldn't find a way to apply what I saw in this question and this one.

P.S.: in constructors, is it preferred to use this.FieldName or just FieldName?

I think you forgot to copy the field initialization into the `Regione` constructor. — , Feb 04 '12 at 23:35

score 3 · Accepted Answer · answered Feb 04 '12 at 23:31

Is it correct to use :this() in all constructors of the base class except the one with most parameters, with the others pointing towards the latter?

The only use case is constructor chaining where you minimize your initialization work to one constructor and have all other constructor use this() with parameters that cause that constructor to execute - you are doing exactly this already in your EnteBase class.

An empty base() call is generally useless, since the default base constructor is called by default anyway.

An empty this() call is going the wrong way and generally useless too (unless you have some initialization work that does not depend on the parameters) - you should pass parameters a constructor with more parameters is called, eventually ending up at the one constructor that does all the work.

score 1 · Answer 2 · answered Feb 04 '12 at 23:27

1

Is it correct to use :this() pointing to the base constructor in the classes Provincia and Regione and then assign to the fields from inside the method itself?

In C#, a call to :base() is implicit, so it need not be done explicitly.

As a consequence of this, in your examples, you do not need the call to :this() since all this does is call the base parameterless constructor.

Is it correct to use :this() in all constructors of the base class except the one with most parameters, with the others pointing towards the latter?

This is a common way of giving values sensible defaults, yes.

answered Feb 04 '12 at 23:27

Rich O'Kelly

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Is your first answer still valid for the class `Regione` now that I've used the parameterless constructor to initialize `this.Province`? If no, what should change? – kettlepot Feb 04 '12 at 23:41
@GabrieleCirulli You'll need to keep the call to `:this()`, or alternatively, initialise a backing field for the property inline. – Rich O'Kelly Feb 04 '12 at 23:44
is that the usual `private List province = new List()`? – kettlepot Feb 04 '12 at 23:48
@GabrieleCirulli Yep - you got it! – Rich O'Kelly Feb 05 '12 at 00:04

Alex · Answer 3 · 2012-02-04T23:38:22.090

You should change the following Constructor in the subclass from:

public Provincia ( string nome, int numeroComuni )
    : this()
{
    this.Nome = nome;
    this.NumeroComuni = numeroComuni;
}

To:

public Provincia ( string nome, int numeroComuni )
    : base(nome, numeroComuni)
{
}

AND the same in the following Constructor, from:

public Provincia( string nome, int numeroComuni, string sigla)
    : this()
{
    this.Nome = nome;
    this.NumeroComuni = numeroComuni;
    this.Sigla = sigla;
}

To:

public Provincia( string nome, int numeroComuni, string sigla)
    : base(nome, numeroComuni)
{
    this.Sigla = sigla;
}

Eliminating the need to set properties of the superclass in the subclass, as intended by the superclasses implementation.

How do I use :base() and :this() correctly?

3 Answers3