Class inheritance constructor questino ...

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Jamie Risk - 28 Jun 2007 22:02 GMT

Two classes:

public class _A {
public int Value1;
public int Value2;

public _A(int v1, int v2) {
this.Value1 = v1;
this.Value2 = v2;
}
}

public class _B : _A {
public int Value3;

public _B(_A a, v3) : base(a.Value1, a.Value2) {
this.Value3 = v3;
}
}

Is there a way I can create a constructor for _B without have to
break apart the elements of the _A typed argument when calling
the base constructor?

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Jon Skeet [C# MVP] - 28 Jun 2007 22:11 GMT

> Two classes:
>
[quoted text clipped - 19 lines]
> break apart the elements of the _A typed argument when calling
> the base constructor?

I'm not sure what you mean - could you elaborate?

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http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
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Peter Duniho - 28 Jun 2007 23:16 GMT

>> Is there a way I can create a constructor for _B without have to
>> break apart the elements of the _A typed argument when calling
>> the base constructor?
>
> I'm not sure what you mean - could you elaborate?

I assume he means he'd like to do "public _B(_A a, v3) : base(a)..." or
something similar even when _A doesn't define a constructor that takes an
instance of an _A.

As far as I know, it's not possible. But I've been wrong before. :)

Pete

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Jon Skeet [C# MVP] - 28 Jun 2007 23:30 GMT

> >> Is there a way I can create a constructor for _B without have to
> >> break apart the elements of the _A typed argument when calling
[quoted text clipped - 7 lines]
>
> As far as I know, it's not possible. But I've been wrong before. :)

Correct. On the other hand, it's perfectly possible for a constructor
to take an instance of the same type and copy field values over etc.

What you also can't do is try to create a new object which still uses
the old object for its base fields, permanently linking the two
together. Of course, you can keep a reference to the old object and
keep referring to it that way, using composition instead of (or as well
as) inheritance.

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Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

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Jamie Risk - 29 Jun 2007 14:29 GMT

> What you also can't do is try to create a new object which still uses
> the old object for its base fields, permanently linking the two
> together.

This exactly what I was trying to ask.

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Peter Duniho - 29 Jun 2007 17:28 GMT

>> What you also can't do is try to create a new object which still uses
>> the old object for its base fields, permanently linking the two
>> together.
>
> This exactly what I was trying to ask.

Really? That wasn't clear _at all_, for what it's worth. Your example
appeared to be asking simply about copying the values from the old object,
not tying the old object permanently to the new one.

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Chris Dunaway - 28 Jun 2007 22:32 GMT

> Two classes:
>
[quoted text clipped - 21 lines]
> break apart the elements of the _A typed argument when calling
> the base constructor?

Add a constructor to your A class that takes an instance of A:

public class _A {

> public int Value1;
> public int Value2;
[quoted text clipped - 3 lines]
> this.Value2 = v2;
> }

//second constructor
public _A(_A a) {
}

Then you can change your _B constructor like this:

> public class _B : _A {
> public int Value3;
[quoted text clipped - 4 lines]
>
> }

I hope I've understood your question correctly.

Chris

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Class inheritance constructor questino ...

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