Polymorphism; simple question

[David Vestal]

Which version of foo() is bar() going to call? I'm not seeing what I
expected to see.

class A{}
class B : A{}
class C
{
public void foo(A a){}
public void foo(B b){}
}

some function bar()
{
C c = new C();
A obj = new B();

c.foo(obj);
}

[Jon Skeet [C# MVP]]

David Vestal <so****************@mailcity.com> wrote:

Which version of foo() is bar() going to call? I'm not seeing what I
expected to see.

class A{}
class B : A{}
class C
{
public void foo(A a){}
public void foo(B b){}
}

some function bar()
{
C c = new C();
A obj = new B();

c.foo(obj);
}

I'd expect foo(A a) to be called. The method signature is determined at
compile time - and at that stage, the compiler only knows that the obj
is an "A" reference.

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

[Serge Bollaerts]

Just for fun...

using System;

namespace FooFooFoo

{

class Class1

{

[STAThread]

static void Main(string[] args)

{

C c = new C();

A obj = new B();

c.foo(obj);

}

}

public class A {}

public class B : A {}

public class C

{

public void foo(A a)

{

System.Diagnostics.Debug.WriteLine("C:foo(A) Has been called");

}

public void foo(B b)

{

System.Diagnostics.Debug.WriteLine("C:foo(B) Has been called");

}

}

}

[Marcin Grzêbski]

Hi David,

Which version of foo() is bar() going to call? I'm not seeing what I
expected to see.

class A{}
class B : A{}
class C
{
// i bet on this call:
public void foo(A a){}
public void foo(B b){}
// add this:
public void foo(object o) {};
} some function bar()
{
C c = new C();
A obj = new B();

c.foo(obj);
// add this:
c.foo((object) new B(); }

Compiler(or whatever it name) takes method with proper parameter
types. So if your object of class B is cast to A or object
then its better to call method with casted types.

Other thing is overriding methods of subclass...

Greetings

Marcin