Question

I’ve been working on a compiler for a custom language for .NET, its currently using System.Reflection.Emit but when I want to run it on Mono (It runs fine on MS .NET, both 2.0 and 4.0 CLRs) I run into a bunch of exceptions when dealing with GenericTypeParameterBuilder, most specifically this one:

Unhandled Exception: System.NotSupportedException: The invoked member is not supported in a dynamic module.
at System.Reflection.Emit.TypeBuilder.check_created () [0x00012] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection.Emit\TypeBuilder.cs:1678 
at System.Reflection.Emit.TypeBuilder.InternalResolve () [0x00000] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection.Emit\TypeBuilder.cs:1653 
at System.Reflection.Emit.GenericTypeParameterBuilder.InternalResolve () [0x00000] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection.Emit\GenericTypeParameterBuilder.cs:93 
at System.Reflection.MonoGenericClass.InternalResolve () [0x00021] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection\MonoGenericClass.cs:105 
at System.Reflection.Emit.TypeBuilder.DefineDefaultConstructor (MethodAttributes attributes) [0x00030] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection.Emit\TypeBuilder.cs:484 
at System.Reflection.Emit.TypeBuilder.CreateType () [0x0017f] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.10.9\mcs\class\corlib\System.Reflection.Emit\TypeBuilder.cs:788 
at dotC.CType.CreateType () [0x00000] in <filename unknown>:0 
at dotC.Compiler.Save () [0x00000] in <filename unknown>:0 
at dotC.Compiler.Compile () [0x00000] in <filename unknown>:0 
at dotC.Dev.Program.Main (System.String[] args) [0x00000] in <filename unknown>:0 

Now the code that runs this is pretty involved so it is hard to copy-paste a specific piece of code, but the code structure I am trying to compile looks like this:

public class Foo<T> { }
public class Bar<T> : Foo<T> { }

And the problem happens when I am trying to compile the Bar<T> class which is supposed to inherit from Foo<T> where the generic parameter supplied to Foo is the T from bar.

So my question is: Is this a known issue in Mono SRE? Is there a way to work around this? Is it fixed in a new beta of mono or something, etc.?

Answer 1

This certainly looks like a bug. It appears that explicitly calling DefineDefaultConstructor on the child type’s type builder prior to setting the parent type and calling CreateType will work around it, at least in the simplest case.

EDIT

Alternatively, explicitly defining a constructor for the child type (which potentially just calls the base constructor and returns) looks like it works even after setting the parent type, so that may be a better approach.