Build c# Generic Type definition at runtime

by

MakeGenericType – i.e.

Type passInType = ... /// perhaps myAssembly.GetType(
        "ConsoleApplication2.Program+Person")
Type t = typeof(List<>).MakeGenericType(passInType);

For a complete example:

using System;
using System.Collections.Generic;
using System.Reflection;
namespace ConsoleApplication2 {
 class Program {
   class Person {}
   static void Main(){
       Assembly myAssembly = typeof(Program).Assembly;
       Type passInType = myAssembly.GetType(
           "ConsoleApplication2.Program+Person");
       Type t = typeof(List<>).MakeGenericType(passInType);
   }
 }
}

As suggested in the comments – to explain, List<> is the open generic type – i.e. “List<T> without any specific T” (for multiple generic types, you just use commas – i.e. Dictionary<,>). When a T is specified (either through code, or via MakeGenericType) we get the closed generic type – for example, List<int>.

When using MakeGenericType, any generic type constraints are still enforced, but simply at runtime rather than at compile time.

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