Should this type of method overload work in C#?

[Dave Raskin]

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(Subclass derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}

I expect this to work, but I tested it at runtime, verifying that the
instance is of the Derived class and it still calls the signature with the
base class.

thanks,

Dave Raskin

[Flip]

Howdy. I believe I got it to work properly (as you expected) for me.
Here's the code I used (slightly modified to get it to compile). Output at
the end.
//--------------------------------------------------------------start code
using System;

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.WriteLi ne("Called public void Send(Base baseObject) signature");
}

public void Send(Derived derivedObject)
{
// send derivedObject
Console.WriteLi ne("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}
//--------------------------------------------------------------end code
And here's the output I see.

C:\temp>basetes ting
Called public void Send(Base baseObject) signature
Called public void Send(Subclass derivedObject) signature

C:\temp>

[Flip]

Howdy. I believe I got it to work properly (as you expected) for me.
Here's the code I used (slightly modified to get it to compile). Output at
the end.
//--------------------------------------------------------------start code
using System;

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.WriteLi ne("Called public void Send(Base baseObject) signature");
}

public void Send(Derived derivedObject)
{
// send derivedObject
Console.WriteLi ne("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}
//--------------------------------------------------------------end code
And here's the output I see.

C:\temp>basetes ting
Called public void Send(Base baseObject) signature
Called public void Send(Subclass derivedObject) signature

C:\temp>

[Joe Mayo]

Hi Dave,

Service doesn't have an overload with a Derived parameter, so the compiler
used a best match that took the overload with the Base parameter. From the
information you've given, I can't tell what SubClass is. However, if you
change the definition of Send(SubClass derivedObject) to this, you could get
what you expect:

public void Send(Derived derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Derived derivedObject)
signature");
}

Joe
--
http://www.csharp-station.com

"Dave Raskin" <Dave Ra****@discussi ons.microsoft.c om> wrote in message
news:0A******** *************** ***********@mic rosoft.com...

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(Subclass derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}

I expect this to work, but I tested it at runtime, verifying that the
instance is of the Derived class and it still calls the signature with the
base class.

thanks,

Dave Raskin

[Joe Mayo]

Hi Dave,

Service doesn't have an overload with a Derived parameter, so the compiler
used a best match that took the overload with the Base parameter. From the
information you've given, I can't tell what SubClass is. However, if you
change the definition of Send(SubClass derivedObject) to this, you could get
what you expect:

public void Send(Derived derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Derived derivedObject)
signature");
}

Joe
--
http://www.csharp-station.com

"Dave Raskin" <Dave Ra****@discussi ons.microsoft.c om> wrote in message
news:0A******** *************** ***********@mic rosoft.com...

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(Subclass derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}

I expect this to work, but I tested it at runtime, verifying that the
instance is of the Derived class and it still calls the signature with the
base class.

thanks,

Dave Raskin

[Dave Raskin]

You're right, the second Send() signautre should have Derived as param, not
Subclass.

Thanks for your answer. My case didn't work, although what I presented here
is a simplified situation, which I thought was essentially the same, but may
be I missed something. I will take a look.

"Flip" wrote:

Howdy. I believe I got it to work properly (as you expected) for me.
Here's the code I used (slightly modified to get it to compile). Output at
the end.
//--------------------------------------------------------------start code
using System;

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.WriteLi ne("Called public void Send(Base baseObject) signature");
}

public void Send(Derived derivedObject)
{
// send derivedObject
Console.WriteLi ne("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}
//--------------------------------------------------------------end code
And here's the output I see.

C:\temp>basetes ting
Called public void Send(Base baseObject) signature
Called public void Send(Subclass derivedObject) signature

C:\temp>

[Dave Raskin]

You're right, the second Send() signautre should have Derived as param, not
Subclass.

Thanks for your answer. My case didn't work, although what I presented here
is a simplified situation, which I thought was essentially the same, but may
be I missed something. I will take a look.

"Flip" wrote:

Howdy. I believe I got it to work properly (as you expected) for me.
Here's the code I used (slightly modified to get it to compile). Output at
the end.
//--------------------------------------------------------------start code
using System;

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.WriteLi ne("Called public void Send(Base baseObject) signature");
}

public void Send(Derived derivedObject)
{
// send derivedObject
Console.WriteLi ne("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}
//--------------------------------------------------------------end code
And here's the output I see.

C:\temp>basetes ting
Called public void Send(Base baseObject) signature
Called public void Send(Subclass derivedObject) signature

C:\temp>

[Dave Raskin]

The signature with Subclass should be with Derived, sorry.

"Joe Mayo" wrote:

Hi Dave,

Service doesn't have an overload with a Derived parameter, so the compiler
used a best match that took the overload with the Base parameter. From the
information you've given, I can't tell what SubClass is. However, if you
change the definition of Send(SubClass derivedObject) to this, you could get
what you expect:

public void Send(Derived derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Derived derivedObject)
signature");
}

Joe
--
http://www.csharp-station.com

"Dave Raskin" <Dave Ra****@discussi ons.microsoft.c om> wrote in message
news:0A******** *************** ***********@mic rosoft.com...

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(Subclass derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}

I expect this to work, but I tested it at runtime, verifying that the
instance is of the Derived class and it still calls the signature with the
base class.

thanks,

Dave Raskin

[Dave Raskin]

The signature with Subclass should be with Derived, sorry.

"Joe Mayo" wrote:

Hi Dave,

Service doesn't have an overload with a Derived parameter, so the compiler
used a best match that took the overload with the Base parameter. From the
information you've given, I can't tell what SubClass is. However, if you
change the definition of Send(SubClass derivedObject) to this, you could get
what you expect:

public void Send(Derived derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Derived derivedObject)
signature");
}

Joe
--
http://www.csharp-station.com

"Dave Raskin" <Dave Ra****@discussi ons.microsoft.c om> wrote in message
news:0A******** *************** ***********@mic rosoft.com...

public class Base
{
}

public class Derived : Base
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(Subclass derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(Subclass derivedObject)
signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
Base baseObject = new Base();
Derived derivedObject = new Derived();

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
service.Send(ba seObject);

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
service.Send(de rivedObject);
}
}

I expect this to work, but I tested it at runtime, verifying that the
instance is of the Derived class and it still calls the signature with the
base class.

thanks,

Dave Raskin

[Dave Raskin]

Ok, here's an example of where it fails. This has an added wrinkle of another
virtual method - Process().

public abstract class Base
{
protected Service service = new Service();

public abstract void Process();
}

public class BaseDerived : Base
{
public override void Process()
{
this.service.Se nd(this);
}
}

public class DerivedDerived : BaseDerived
{
}

public class Service
{
public void Send(Base baseObject)
{
// send baseObject
Console.Out.Wri teLine("Called public void Send(Base baseObject)
signature");
}

public void Send(DerivedDer ived derivedObject)
{
// send derivedObject
Console.Out.Wri teLine("Called public void Send(DerivedDer ived
derivedObject) signature");
}
}

public class MainClass
{
public static void Main(string[] args)
{
BaseDerived baseObject = new BaseDerived();
DerivedDerived derivedObject = new DerivedDerived( );

Service service = new Service();

// this calls public void Send(Base baseObject) as expected
baseObject.Proc ess();

// this calls public void Send(Base baseObject),
// but it should call public void Send(Subclass derivedObject),
// shouldn't it???
derivedObject.P rocess();
}
}