Get all types implementing specific open generic type

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 {} 

Answer 2

Solution implemented without LINQ, searching both generic and non generic interfaces, filtering the return type to classes.

public static class SampleCode {     public static void Main()     {         IList<Type> loadableTypes;          // instance the dummy class used to find the current assembly         DummyClass dc = new DummyClass();          loadableTypes = GetClassesImplementingAnInterface(dc.GetType().Assembly, typeof(IMsgXX)).Item2;         foreach (var item in loadableTypes) {Console.WriteLine("1: " + item);}         // print         // 1: Start2.MessageHandlerXY          loadableTypes = GetClassesImplementingAnInterface(dc.GetType().Assembly, typeof(IHandleMessageG<>)).Item2;         foreach (var item in loadableTypes) { Console.WriteLine("2: " + item); }         // print         // 2: Start2.MessageHandlerXY         // 2: Start2.MessageHandlerZZ     }      ///<summary>Read all classes in an assembly that implement an interface (generic, or not generic)</summary>     //     // some references     // return all types implementing an interface     // http://stackoverflow.com/questions/26733/getting-all-types-that-implement-an-interface/12602220#12602220     // http://haacked.com/archive/2012/07/23/get-all-types-in-an-assembly.aspx/     // http://stackoverflow.com/questions/7889228/how-to-prevent-reflectiontypeloadexception-when-calling-assembly-gettypes     // return all types implementing a generic interface     // http://stackoverflow.com/questions/33694960/find-all-types-implementing-a-certain-generic-interface-with-specific-t-type     // http://stackoverflow.com/questions/8645430/get-all-types-implementing-specific-open-generic-type     // http://stackoverflow.com/questions/1121834/finding-out-if-a-type-implements-a-generic-interface     // http://stackoverflow.com/questions/5849210/net-getting-all-implementations-of-a-generic-interface     public static Tuple<bool, IList<Type>> GetClassesImplementingAnInterface(Assembly assemblyToScan, Type implementedInterface)     {         if (assemblyToScan == null)             return Tuple.Create(false, (IList<Type>)null);          if (implementedInterface == null || !implementedInterface.IsInterface)             return Tuple.Create(false, (IList<Type>)null);          IEnumerable<Type> typesInTheAssembly;          try         {             typesInTheAssembly = assemblyToScan.GetTypes();         }         catch (ReflectionTypeLoadException e)         {             typesInTheAssembly = e.Types.Where(t => t != null);         }          IList<Type> classesImplementingInterface = new List<Type>();          // if the interface is a generic interface         if (implementedInterface.IsGenericType)         {             foreach (var typeInTheAssembly in typesInTheAssembly)             {                 if (typeInTheAssembly.IsClass)                 {                     var typeInterfaces = typeInTheAssembly.GetInterfaces();                     foreach (var typeInterface in typeInterfaces)                     {                         if (typeInterface.IsGenericType)                         {                             var typeGenericInterface = typeInterface.GetGenericTypeDefinition();                             var implementedGenericInterface = implementedInterface.GetGenericTypeDefinition();                              if (typeGenericInterface == implementedGenericInterface)                             {                                 classesImplementingInterface.Add(typeInTheAssembly);                             }                         }                     }                 }             }         }         else         {             foreach (var typeInTheAssembly in typesInTheAssembly)             {                 if (typeInTheAssembly.IsClass)                 {                     // if the interface is a non-generic interface                     if (implementedInterface.IsAssignableFrom(typeInTheAssembly))                     {                         classesImplementingInterface.Add(typeInTheAssembly);                     }                 }             }         }         return Tuple.Create(true, classesImplementingInterface);     } }  public class DummyClass { }  public interface IHandleMessageG<T> { }  public interface IHandleMessage { }  public interface IMsgXX { }  public interface IMsgXY { }  public interface IMsgZZ { }  public class MessageHandlerXY : IHandleMessageG<IMsgXY>, IHandleMessage, IMsgXX {     public string Handle(string a)     {         return "aaa";     } }  public class MessageHandlerZZ : IHandleMessageG<IMsgZZ>, IHandleMessage {     public string Handle(string a)     {         return "bbb";     } }