delegates and virtual functions

[puzzlecracker]

Do delegates don't respect polymorphisms -- why?

say in this example:

using System;

public delegate string FirstDelegate (int x);
abstract class Base
{
public abstract string Foo(int );

public void Dispatch()
{
FirstDelegate del=new FirstDelegate (Foo);
del(5);
}
}

class Derived
{
public override string Foo(int x)
{
return " "+x;
}
}
class Runner
{

public static void Main()
{
Derived d=new Derived();
d.Dispatch(); //trys to delegate bases
}
}
The same thing happens when Base is NOT abstract class and Foo is
declared as virtual....

Is there a rule don't mix delegates and runtime polymorphism???

[Marc Gravell]

What same thing? Unfortunately, you haven't pasted the exact code [it
doesn't compile...], so we can't know what you are seeing, since any
repairs we make may change the problem...

However, making the most obvious fixes (adding a base class, naming
the argument, etc) - it all works fine and the override in Derived is
called.

Delegates respect polymorphism.

Perhaps tell us what you are seeing?

Marc
[C# MVP]

[Philipp Brune]

Hi,

why should delegates not respect polymorphisms ?
This code, works as expected for me. FirstDelegate
points to the implementation of Foo(..) in Derived.
The only thing that leads to a StackOverflowException is
doing

class DerivedOverflow : Derived
{
public override string Foo(int x)
{
return "-" + base.Dispatch();
}
}

which is also expected behaviour from my understandings.

Perhaps you could explain a little more what you mean.

Philipp

puzzlecracker schrieb:

Do delegates don't respect polymorphisms -- why?

say in this example:

using System;

public delegate string FirstDelegate (int x);
abstract class Base
{
public abstract string Foo(int );

public void Dispatch()
{
FirstDelegate del=new FirstDelegate (Foo);
del(5);
}
}

class Derived
{
public override string Foo(int x)
{
return " "+x;
}
}
class Runner
{

public static void Main()
{
Derived d=new Derived();
d.Dispatch(); //trys to delegate bases
}
}
The same thing happens when Base is NOT abstract class and Foo is
declared as virtual....

Is there a rule don't mix delegates and runtime polymorphism???

[puzzlecracker]

On Oct 21, 10:06*am, Philipp Brune <[e-mail]:

Hi,

why should delegates not respect polymorphisms ?
This code, works as expected for me. FirstDelegate
points to the implementation of Foo(..) in Derived.
The only thing that leads to a StackOverflowException is
doing

* class DerivedOverflow : Derived
* * *{
* * * * *public override string Foo(int x)
* * * * *{
* * * * * * *return "-" + base.Dispatch();
* * * * *}
* * *}

which is also expected behaviour from my understandings.

Perhaps you could explain a little more what you mean.

Philipp

puzzlecracker schrieb:

Do delegates don't respect polymorphisms -- why?

say in this example:

using System;

public delegate string FirstDelegate (int x);

abstract class Base
{
*public abstract string *Foo(int );

* * * public void Dispatch()
* * * {
* * * * * * FirstDelegate *del=new FirstDelegate (Foo);
* * * * * * del(5);
* * }
}

class Derived
{
* * *public override string *Foo(int x)
* * * {
* * * * * *return " "+x;
* * *}
}

class Runner
{

* * * * public static void Main()
* * * * {
* * * * * * * Derived d=new Derived();
* * * * * * * d.Dispatch(); //trys to delegate bases
* * * * }
}

The same thing happens when Base is NOT abstract class and Foo is
declared as virtual....

Is there a rule don't mix delegates and runtime polymorphism???

Great! let me get the debug, i thing my telling compiler to think
Base is Base.....