Today I was adding some new logic to some older code and I noticed there was very little test coverage on the logic so I decided to add some.  As I was adding coverage I wanted to add some tests that proved out our Contract style bound checks.  However there was one slight problem.  The method(s) I wanted to add coverage to was overloaded as such:

public virtual IMessageTransporter GetTransporter( Destination destination )
{
    // The null transporter will allow for testing without hittng rhapsody or an engine
    if ( ConfigurationReader.UseNullTransporter ) { return new NullTransporter(); }

    Contracts.Requires( destination != null );
    
    // for now we only have one transporter for now.... will add more later
    return new HttpTransporter( destination.Endpoint );

}

and

public virtual IMessageTransporter GetTransporter( Endpoint endpoint )
{
    // The null transporter will allow for testing without hittng rhapsody or an engine
    if ( ConfigurationReader.UseNullTransporter ) { return new NullTransporter(); }

    Contracts.Requires( endpoint != null );
    
    // for now we only have one transporter for now.... will add more later
    return new HttpTransporter( endpoint  );

}

As you can see from the 2 methods above they are the same with ONLY the provided parameter being different.  When I started to write my tests I did this:

transporterFactory.GetTransporter( null );

But when I simply added NULL as the parameter the compiler provided me the following error

The call is ambiguous between the following methods or properties: ‘TransporterFactory.GetTransporter(Destination)' and TransporterFactory.GetTransporter(Endpoint)'    C:\PathHere\TransporterFactoryTests.cs    13    45    Common.Tests

Now if you think about it for even 2 seconds the above error makes perfect sense.  So the real question is how do you get around this….?  Simple you do the following.

transporterFactory.GetTransporter( (Destination)null );

By providing a type on your call the compiler now will know which overload you are attempting to call and the world will be a happier place.

Till next time,