C# Generics Constraints: Is there a way to express is not a?

Question

I have the following code:

interface IConverter<T, U>
{
    U Convert(T obj);
}

interface IBusinessEntityConveter<T, U> : IConverter<T, U>
    where U : BusinessEntity
{
}

class LookupConveter<B> : IBusinessEntityConveter<Lookup, B>, IConverter<Lookup, Moniker>
    where B : BusinessEntity, new()
{

    #region IConverter<Lookup, Moniker> Members

    public Moniker Convert(Lookup obj)
    {
       //...
    }

    #endregion


    #region IConverter<Lookup,B> Members

    public B Convert(Lookup obj)
    {
       //...
    }

    #endregion
}

I am getting this error:

Error 2 'Convertors.LookupConveter<B>' cannot implement both 'Convertors.IConverter<Microsoft.Crm.Sdk.Lookup,B>' and 'Convertors.IConverter<Microsoft.Crm.Sdk.Lookup,Microsoft.Crm.Sdk.Moniker>' because they may unify for some type parameter substitutions

Is there a way to specify that T isn't a business entity?

Answer 1

Nope, I'm afraid not. The only options you have are listed here Constraints on Type Parameters. In summary these are:

• enforce a value type
• enforce a reference type
• enforce a non reference type, which contains no reference types
• enforce a public parameterless constructor
• enforce a specific base class
• enforce a specific interface
• enforce type derives from an argument

Answer 2

No, there are no "negative" constraints.