C#: IL/Emit: DynamicMethod and DateTime problem

[joasi]

Hi,
I am working in C# with an Object / Relational Database mapping framework, where I want to generate method calls based on string representation of the call signature.
I have used reflection and Method-/Field-/PropertyInfo invokation to do this, but now I want to make the calls faster by using Emit and DynamicMethods

I am now trying to create a factory method that creates a dynamic method as a "wrapper" around a method call with no arguments.
The type of object to call the method on is passed as a parameter to the dynamicMethod factory method
The name of the method to wrap is passed as a string, by which I get the MethodInfo-object for the method.
The generated dynamic method is returned as a delegate, which I later invoke with the particular object that I want to call the wrapped method on.

The solution seems to work fine except for DateTime: If I pass DateTime as the type and "ToShortDateStr ing()" as the method signature I get a completely different datetime-string than expected: for example "6884-12-07" instead of 2008 something.

The code I use to generate the dynamic method is as follows:

using System;
using System.Reflection;
using System.Reflection.Emit;

...

public delegate object GetHandler(object source);

internal static GetHandler CreateGetHandler(Type type, MethodInfo methodInfo)
{
   DynamicMethod dynamicGet = CreateGetDynamicMethod(type, methodInfo.Name);
   ILGenerator getGenerator = dynamicGet.GetILGenerator();
   getGenerator.Emit(OpCodes.Ldarg_0);
   getGenerator.Emit(OpCodes.Call, methodInfo);
   getGenerator.Emit(OpCodes.Ret);
   return (GetHandler)dynamicGet.CreateDelegate(typeof(GetHandler));
}

...

private static DynamicMethod CreateGetDynamicMethod(Type type, string name)
{
   return new DynamicMethod("Dynamic" + name, typeof(object), new Type[] { typeof(object) }, type, true);
}

I have tried box/unboxing argument and return value without any effect. Can anyone see what I am doing wrong or is this a bugg in DateTime or Emit?

Thanks,

/Joakim

[joasi]

After a lot of trial and error I found the answer:

Any ValueType-object that is passed boxed as an object to the DynamicMethod factory has to be (in IL) first loaded to the stack as a value from the argument, then unboxed, then stored to a local variable declared as the ValueType, and finally loaded as a reference to the stack.
Then the method call can be invoked on the boxed object reference.

this is the code I came up with:

internal static GetHandler CreateGetHandler(Type type, MethodInfo methodInfo)
{
   DynamicMethod dynamicGet = CreateGetDynamicMethod(type, methodInfo.Name);
   ILGenerator getGenerator = dynamicGet.GetILGenerator();
   getGenerator.Emit(OpCodes.Ldarg_0);
   if (type.IsValueType)
   {
      getGenerator.DeclareLocal(type);
      getGenerator.Emit(OpCodes.Unbox_Any, type);
      getGenerator.Emit(OpCodes.Stloc_0);
      getGenerator.Emit(OpCodes.Ldloca_S, 0);
   }
   getGenerator.Emit(OpCodes.Callvirt, methodInfo);
   if (methodInfo.ReturnType.IsValueType)
   {
      getGenerator.Emit(OpCodes.Box, methodInfo.ReturnType);
   }
   getGenerator.Emit(OpCodes.Ret);
   return (GetHandler)dynamicGet.CreateDelegate(typeof(GetHandler));
}

[Alxandr]

Sorry to tell you, but you can skipp the storing and loading, and only do the unboxing. I've written a tutorial on it here: http://alxen.wordpress.com/2010/10/1...t-and-opcodes/