Implementing interface, returning subclass

[Guest]

Hi;

I am writing a class that implements IDbConnection. The i/f defines a methof
BeginTransaction() that returns an IDbTransaction. I want to define this as
returning a DbTransaction (as DbConnection does). It makes sense to me that
this is legal as DbTransaction implements IDbTransaction so it does meet the
contract of returning an IDbTransaction.

But it won't compile - how do I get this to work? (There must be a way as
DbConnection does it.)

 

[Mattias Sjögren]

David,

But it won't compile - how do I get this to work? (There must be a way as
DbConnection does it.)

Something like this, using explicit implementation

IDbTransaction IDbConnection.BeginTransaction()
{
return BeginTransaction();
}

public DbTransaction BeginTransaction()
{
// ...
}


Mattias

 

[David Browne]

Hi;

I am writing a class that implements IDbConnection. The i/f defines a
methof
BeginTransaction() that returns an IDbTransaction. I want to define this
as
returning a DbTransaction (as DbConnection does). It makes sense to me
that
this is legal as DbTransaction implements IDbTransaction so it does meet
the
contract of returning an IDbTransaction.

But it won't compile - how do I get this to work? (There must be a way as
DbConnection does it.)

You can return a DbTransaction if you like, but the method must be declared
as returning IDbTransaction. And you can always use explicit interface
implementation to hide all of th IDbConnection interface methods.

David

 

[Guest]

Hi;

I tried explicit but the error message says it is for operators only and I
need this for a property. And it won't let me have two properties with the
same name and differing only in return type.

Any other approaches?

 

[Mattias Sjögren]

David,

I tried explicit but the error message says it is for operators only and I
need this for a property. And it won't let me have two properties with the
same name and differing only in return type.

Did you try the code I posted? It doesn't use the explicit keyword,
and I didn't mean to imply that you should. I'm talking about explicit
interface implementation:

http://msdn.microsoft.com/library/en-us/csref/html/vcwlkExplicitInterfaceImplementationTutorial.asp


Mattias