Using delegate/DLR Lambdas to override instance methods? - f#

Question

In an effort to learn F# and .Net, I've been playing around with the to-be-released DLR.
To that end, I've been playing around with reflection, in an effort to implement a basic type system that integrates nicely with the clr. While I'm able to instantiate a simple type that extends Object, I get an error when calling the method it defines.
Because at the end of the day DLR LambdaExpressions compile down to delegates, what I do is take generated MethodInfo off the generated delegate and call it, populating the stack with the args of the generated method. Then return it. It's at this point I get my error.
Here's my code:
open System
open System.Reflection
open System.Reflection.Emit
type ConstructorInformation=
{Types:System.Type array}
type MethodInformation=
{ParamTypes:System.Type array;
Name:string
Impl:System.Delegate}
let rec addConstructors (t:TypeBuilder) (baseType:System.Type) constructorInfos =
match constructorInfos with
|ci::rest ->
let cb = t.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard,ci.Types)
let ilGen = cb.GetILGenerator()
ilGen.Emit(OpCodes.Ldarg_0)
Array.iteri (fun (index:int) _-> ilGen.Emit(OpCodes.Ldarg, index+1)) ci.Types
ilGen.Emit( OpCodes.Call, baseType.GetConstructor(ci.Types) )
addConstructors t baseType rest
|[] -> ()
let rec addMethods (tb:TypeBuilder) baseType methodInfos =
match methodInfos with
|mi::rest ->
let mb = tb.DefineMethod(mi.Name, MethodAttributes.Public, typeof<obj>, mi.ParamTypes)
let ilGen = mb.GetILGenerator()
ilGen.Emit(OpCodes.Ldarg_0)
Array.iteri (fun index _ -> ilGen.Emit(OpCodes.Ldarg, index+1)) mi.ParamTypes
ilGen.EmitCall(OpCodes.Call, mi.Impl.Method, mi.ParamTypes)
ilGen.Emit(OpCodes.Ret)
addMethods tb baseType rest
|[] -> ()
let defineType (baseType:System.Type) constructorInfos methodInfos=
let ab = AppDomain.CurrentDomain.DefineDynamicAssembly( AssemblyName("test"), AssemblyBuilderAccess.Run)
let mb = ab.DefineDynamicModule("test")
let typeBuilder = mb.DefineType("testType", TypeAttributes.Public, baseType)// | TypeAttributes.Class
addConstructors typeBuilder baseType constructorInfos
addMethods typeBuilder baseType methodInfos
typeBuilder.CreateType()
type Delegate1 = delegate of obj -> obj
let echo y:#obj= (y :> obj)
let del1 : Delegate1 = new Delegate1(echo)
let mis:MethodInformation list=[{Impl=del1; Name="Echo"; ParamTypes=[|(typeof<obj>)|]}]
let cis:ConstructorInformation list=[]
let t= defineType (typeof<obj>) cis mis
let cinfo = t.GetConstructor([||])
let instance =cinfo.Invoke([||])
instance.GetType()
(t.GetMethod("Echo")).Invoke(instance, [| (1:>obj)|])
Here's my error, from fsi:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.MethodAccessException: clo#51.Invoke(System.Object)
at testType.Echo(Object )
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at <StartupCode$FSI_0002>.$FSI_0002._main()
stopped due to error
Any help or suggestions would be appreciated-I'm a bit of a .Net newb so my mistake may be simple.
Mike Kohout

Answer 1

Well, I solved it. The generated cil was bad. Also, I had to dynamicinvoke on the delegate, not the function it was fronting.
#light
open System
open System.Reflection
open System.Reflection.Emit
type ConstructorInformation=
{Types:System.Type array}
type MethodInformation=
{ParamTypes:System.Type array;
Name:string;
Impl:System.Delegate;
mutable Field:FieldBuilder option}
let rec addConstructors (t:TypeBuilder) (baseType:System.Type) constructorInfos =
match constructorInfos with
|ci::rest ->
let cb = t.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard,ci.Types)
let ilGen = cb.GetILGenerator()
ilGen.Emit(OpCodes.Ldarg_0)
Array.iteri (fun (index:int) _-> ilGen.Emit(OpCodes.Ldarg, index+1)) ci.Types
ilGen.Emit( OpCodes.Call, baseType.GetConstructor(ci.Types) )
addConstructors t baseType rest
|[] -> ()
let rec addMethods (tb:TypeBuilder) baseType methodInfos =
match methodInfos with
|mi::rest ->
let fb = tb.DefineField(mi.Name+"_field", typeof<Delegate>, FieldAttributes.Public);
mi.Field <- Some(fb)
let mb = tb.DefineMethod(mi.Name, MethodAttributes.Public, typeof<obj>, mi.ParamTypes)
let ilGen = mb.GetILGenerator()
let arrayLocal = ilGen.DeclareLocal((typeof<obj[]>))
ilGen.Emit(OpCodes.Ldarg_0)
ilGen.Emit(OpCodes.Ldfld, fb)
ilGen.Emit(OpCodes.Ldc_I4, Array.length mi.ParamTypes)
ilGen.Emit(OpCodes.Newarr, typeof<obj>)
ilGen.Emit(OpCodes.Stloc, arrayLocal)
ilGen.Emit(OpCodes.Ldloc, arrayLocal)
Array.iteri (fun index _ -> ilGen.Emit(OpCodes.Ldc_I4, index)
ilGen.Emit(OpCodes.Ldarg, index+1)
ilGen.Emit(OpCodes.Stelem_Ref)
ilGen.Emit(OpCodes.Ldloc, arrayLocal)) mi.ParamTypes
ilGen.EmitCall(OpCodes.Callvirt, (mi.Impl.GetType()).GetMethod("DynamicInvoke", [|(typeof<obj[]>)|]), mi.ParamTypes)
ilGen.Emit(OpCodes.Ret)
addMethods tb baseType rest
|[] -> ()
let defineType (baseType:System.Type) constructorInfos methodInfos=
let ab = AppDomain.CurrentDomain.DefineDynamicAssembly( AssemblyName("test"), AssemblyBuilderAccess.Run)
let mb = ab.DefineDynamicModule("test")
let typeBuilder = mb.DefineType("testType", TypeAttributes.Public, baseType)// | TypeAttributes.Class
addConstructors typeBuilder baseType constructorInfos
addMethods typeBuilder baseType methodInfos
typeBuilder.CreateType()
type Delegate1 = delegate of obj -> obj
let echo y:#obj= (y :> obj)
let del1 : Delegate1 = new Delegate1(echo)
type Delegate2 = delegate of obj * obj -> obj
let echoFirst (x:#obj) (y:#obj)=(x:>obj)
let echoFirstDelegate:Delegate2 = new Delegate2(echoFirst)
echoFirstDelegate.DynamicInvoke( [|(1:>obj);(2:>obj)|])
//let mis:MethodInformation list=[{Impl=del1; Name="Echo"; ParamTypes=[|(typeof<obj>)|];Field=None}]
//let cis:ConstructorInformation list=[]
//let t= defineType (typeof<obj>) cis mis
//let cinfo = t.GetConstructor([||])
//let instance =cinfo.Invoke([||])
//instance.GetType()
//(t.GetField("Echo_field")).SetValue(instance, del1)
//let fieldDelegate = (t.GetField("Echo_field")).GetValue(instance) :?> Delegate
//(t.GetMethod("Echo")).Invoke(instance, [| (1:>obj)|])
//del1.DynamicInvoke( [|(1:>obj)|])
let mis:MethodInformation list=[{Impl=del1; Name="Echo"; ParamTypes=[|(typeof<obj>)|];Field=None};
{Impl=echoFirstDelegate; Name="EchoFirst"; ParamTypes=[| (typeof<obj>);(typeof<obj>)|]; Field=None}]
let cis:ConstructorInformation list=[]
let t= defineType (typeof<obj>) cis mis
let cinfo = t.GetConstructor([||])
let instance =cinfo.Invoke([||])
instance.GetType()
(t.GetField("Echo_field")).SetValue(instance, del1)
let fieldDelegate = (t.GetField("Echo_field")).GetValue(instance) :?> Delegate
(t.GetMethod("Echo")).Invoke(instance, [| (1:>obj)|])
(t.GetField("EchoFirst_field")).SetValue(instance, echoFirstDelegate)
(t.GetMethod("EchoFirst")).Invoke(instance, [| (1:>obj);(2:>obj)|])