Question

How do I get all types that implementing a specific open generic type?

For instance:

public interface IUserRepository : IRepository<User>

Find all types that implement IRepository<>.

public static IEnumerable<Type> GetAllTypesImplementingOpenGenericType(Type openGenericType, Assembly assembly)
{
  ...
}

Answer 1

This will return all types that inherit a generic base class. Not all types that inherit a generic interface.

var AllTypesOfIRepository = from x in Assembly.GetAssembly(typeof(AnyTypeInTargetAssembly)).GetTypes()
 let y = x.BaseType
 where !x.IsAbstract && !x.IsInterface &&
 y != null && y.IsGenericType &&
 y.GetGenericTypeDefinition() == typeof(IRepository<>)
 select x;

This will return all types, including interfaces, abstracts, and concrete types that have the open generic type in its inheritance chain.

public static IEnumerable<Type> GetAllTypesImplementingOpenGenericType(Type openGenericType, Assembly assembly)
{
    return from x in assembly.GetTypes()
            from z in x.GetInterfaces()
            let y = x.BaseType
            where
            (y != null && y.IsGenericType &&
            openGenericType.IsAssignableFrom(y.GetGenericTypeDefinition())) ||
            (z.IsGenericType &&
            openGenericType.IsAssignableFrom(z.GetGenericTypeDefinition()))
            select x;
}

This second method will find ConcreteUserRepo and IUserRepository in this example:

public class ConcreteUserRepo : IUserRepository
{}

public interface IUserRepository : IRepository<User>
{}

public interface IRepository<User>
{}

public class User
{}