Bug 39700 - Different behavior for RuntimeType.GetGenericTypeDefinition() between Mono and Windows
Summary: Different behavior for RuntimeType.GetGenericTypeDefinition() between Mono an...
Alias: None
Product: Runtime
Classification: Mono
Component: Reflection ()
Version: 4.2.0 (C6)
Hardware: PC Linux
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2016-03-16 22:19 UTC by Jeremy Meng
Modified: 2016-03-22 18:17 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Jeremy Meng 2016-03-16 22:19:36 UTC
1. Compile and run the following Program.cs, targeting .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Linq;

namespace ConsoleApplication
    public class Program
        public static void Main(string[] args)
            var method = typeof(MyOwnClass).GetMethod("Foo");
            var parameter = method.GetParameters()[0].ParameterType.GetElementType();
            var genericTypeDefinition = parameter.GetGenericTypeDefinition();

    public abstract class MyOwnClass
        public virtual void Foo<T>(List<T>[] action)

        /* ... */


Mono output:


Windows output:

Comment 1 Zoltan Varga 2016-03-19 11:26:54 UTC
This is not a bug, mono uses a differently named c# type internally to represent type objects. This is an implementation detail.
Comment 2 Jeremy Meng 2016-03-19 17:08:59 UTC
However it caused problem as these two types behaves differently. For example, calling GetTypeInfo() off a Mono type throws as it is not an IReflectableType.

Mono has System.RuntimeType too, just not in this specific code (where T is the open type parameter in an array of a generic type?)
Comment 3 Jeremy Meng 2016-03-19 17:12:10 UTC
This has caused some Castle.Core unit tests to fail only on Mono runtime.
Comment 4 Jeremy Meng 2016-03-22 18:17:36 UTC
It looks like the Castle.Core test failures are caused by a different reason.  See discussion at https://github.com/castleproject/Core/issues/160#issuecomment-199788363.