How do I put a contract on a generic interface?

Question

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

Answer 1

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

Answer 2

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]

Answer 3

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