Inheritance question

[cpastre]

I'm having trouble trying to "override" a method from an inherited interface but return a different data type than is defined by the interface. Here's an example to clarify:

public interface IDataReader {}

public interface IDbCommand
{
IDataReader ExecuteReader();
}

public class MyCommand : IDbCommand
{
public IDataReader ExecuteReader() {return new MyDataReader();} }

public class MyDataReader : IDataReader {}

class Test
{
static void Main(string[] args)
{
MyCommand cmd = new MyCommand();
MyDataReader dr = cmd.ExecuteReader();
}
}

When I compile this I get "Cannot implicitly convert type 'IDataReader' to 'MyDataReader'" at the "MyDataReader dr = ..." line. I use the IDbCommand/IDataReader as an example because I've seen it in the SqlClient. The SqlClient analog to "MyDataReader dr = ...," "SqlDataReader dr = ..." does not produce the same error when compiled. So my question is, how do I modify my code to avoid having to explicitly cast "cmd.ExecuteReader()" to MyDataReader?

Thanks,
Charlie

Charlie Pastre
Transition/1 MAS
cpastre@t1mas.com

 

[cpastre]

Update: Got the solution to this one from another newsgroup:

-----Original Message-----
Sent: Wednesday, November 20, 2002 3:10 PM
To: DOTNET-CX@DISCUSS.DEVELOP.COM
Subject: Re: [DOTNET-CX]

You can work around this to some extent with explicit interface
implementation. For example:

public class MyCommand : IDbCommand
{
IDataReader IDBCommand.ExecuteReader()
{return ExecuteReader();}
public MyDataReader ExecuteReader()
{return new MyDataReader(); }
}

--Peter Golde