Code Contracts: How do I supply a contract class for a generic interface?

Question

I'd like to specify a contract for this generic interface, using Code Contracts:

interface IRandomWriteAccessible<T>
{
    T this[uint index] { set; }
    uint Length { get; }
}

The documentation says to use the ContractClass attribute when specifying a contract for an interface. However, the compiler will complain about this:

[ContractClass(typeof(IRandomWriteAccessibleContract<T>))]
//             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^     <-- compiler error
interface IRandomWriteAccessible<T> { … }

[ContractClassFor(typeof(IRandomWriteAccessible<T>))]
//                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^          <-- compiler error
sealed class IRandomWriteAccessibleContract<T> : IRandomWriteAccessible<T> { … }

It seems that type parameters cannot be used with attributes.

How do I write a contract for my generic interface? Or is this not possible with Code Contracts?

Answer 1

As mentioned by other comments in this question, you should remove the generic type identifier from your attribute usage as it can not be resolved at compile time:

[ContractClass(typeof(IRandomWriteAccessibleContract<>))] 

Answer 2

Good question, but you can see the technical reasons behind this limitation, right?

The reason that you can't specify the ContractClass is because Blah<T> is not a class.

If you can make an interface for a concrete class by specifying a value for T, even though I'm sure this is sub-optimal.