How do I put a contract on a generic interface?

Thu, 26 Feb 2009 11:33:12 Z

Say I have the following interface:

public interface IParser<T>
{
T Parse (string toParse);
}

How do I specify the attributes for the contract class?

My initial thought was:

[ContractClass (typeof (IParserContract<T>))]
public interface IParser<T>
{
T Parse (string toParse);
}

and

[ContractClassFor (typeof (IParser<T>))]
public class IParserContract<T>
{
...
}

But that won't work, because you can't use the generic T argument in the attributes. And leaving the generic argument out won't work, because that doesn't specify the right interface/type.

So, am I missing the proper way of doing this, or is this a limitation?

Cheers,

Geoff

How do I put a contract on a generic interface?

Thu, 26 Feb 2009 15:26:26 Z

Excellent question and we probably should put this into the documentation. For generic interface contracts, the typeof has to refer to the non-instantiated generic type. This is a little known C# feature. It looks as follows:

[ContractClass (typeof (IParserContract<>))]  

public interface IParser<T>  

{  

    T Parse (string toParse);  

}  

[ContractClassFor (typeof (IParser<>))]  

public class IParserContract<T>  

{  

    ...  

}

Note the empty instantiation brackets IParserContract<> and IParser<>.

-MaF

How do I put a contract on a generic interface?

Fri, 27 Feb 2009 00:48:01 Z

For multi-parameter generics, as you might imagine, you can use IFoo<,,,,> -- just drop the generic identifiers, leaving the commas, and you're good to go.

This is also useful in instantiating generic types via reflection. typeof(List<>) returns a valid type awaiting parameterization.

Keith J. Farmer [Idea Entity]

How do I put a contract on a generic interface?

Fri, 27 Feb 2009 10:03:31 Z

Manuel Fahndrich said:

For generic interface contracts, the typeof has to refer to the non-instantiated generic type. This is a little known C# feature.

That's excellent - many thanks. And I thought I knew most of the little-known C# features...!

Cheers,

Geoff