C# Constructor – Why Using ‘This’ Works

cconstruction

I got two classes.

busiObj(created from ancient flat files)
key(provides means to tell busiObjs apart)

key has a c'tor that takes a busiObj

public key(busiObj foo)
{
    bar = foo.someThing;
    [...]
}

I want to create the key in the c'tor of the busiObj

public busiObj(...)
{
    myKey = new key(this);
    [...]
}

However: Why on earth does it work?
I firmly expected the compiler to throw something like:
"You cannot reference an object that is currently being made, duh".

So: How is it that I can reference an object while it is still being constructed?

Best Answer

So: How is it that I can reference an object while it is still being constructed?

Presumably Because it's useful (though in a dangerous way) for exactly the scenario you describe, so the language designers decided to allow it.

Technically, it's not a problem at all: while the object is being constructed, its memory must already be allocated, so you can certainly have a reference to it.

Related Solutions

C# SQL Object-Oriented Design – Sanity Check for In-Memory Object Representations of Database Rows

If you're looking for dynamic runtime polymorphism, have you checked out the dynamic keyword in C# 4.0? If it meets your need, I would imagine it's a lot simpler than what you're trying to do.

See Rob Conery's work with Massive, where he demonstrates how to build a dynamic ORM in C# 4.0 using 400 lines of code.

Creating proxy classes at runtime is not exactly an unprecedented technique, see Castle Dynamic Proxy and FasterFlect. If your only worry is that you're breaking some architectural austronaut's rule book, I'm not sure it's worth worrying about.

C# – Reuse Base Constructor Argument in This Constructor

You can use constructor chaining to pass the dependency to a separate constructor in Derived, and then both pass that to the base constructor and set the field value:

class Base
{
    private BaseComponent component;

    protected Component
    {
        get { return component; }
    }

    Base(BaseComponent component)
}

class Derived : Base
{
    private DerivedComponent component;

    Derived() : this(new DerivedComponent())
    { }

    Derived(DerivedComponent component) : base(component)
    {
        this.component = component;
    }
}

Best Answer

Related Solutions

C# SQL Object-Oriented Design – Sanity Check for In-Memory Object Representations of Database Rows

C# – Reuse Base Constructor Argument in This Constructor

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