Creating a .NET delegate object from an Eiffel routine

by Manu (modified: 2010 Jan 15)

Someone recently asked me how to create a .NET delegate from an Eiffel routine. Ideally it would be nice to simply do:

my_delegate := (agent my_routine).to_delegate

where `to_delegate' is a query from the ROUTINE class. However this feature does not yet exist. Instead I've devised a simple way to create a delegate given a routine name of the Current class:

my_delegate := new_delegate ("my_routine")

Where new_delegate is defined as:

new_delegate (a_name: STRING): DELEGATE -- Using `a_name' routine from the current class creates its corresponding -- .NET delegate if found, Void otherwise. require a_name_not_void: a_name /= Void local l_obj: SYSTEM_OBJECT l_method_info: METHOD_INFO l_params: NATIVE_ARRAY [SYSTEM_TYPE] l_delegate_type: SYSTEM_TYPE i, nb: INTEGER do l_obj := Current -- Obtain the associated MethodInfo for routine `a_name' from Current. -- Use the Eiffel name first and if we cannot find it, then the PascalCase version -- of the name (This is an EiffelStudio project settings for .NET code generation). l_method_info := l_obj.get_type.get_method (a_name) if l_method_info = Void then l_method_info := l_obj.get_type.get_method (pascal_case (a_name)) end -- If not MethodInfo was found, the name was incorrect and we simply return Void. if l_method_info /= Void then if attached l_method_info.get_parameters as l_infos then from i := 0 nb := l_infos.count create l_params.make (nb + 1) until i = nb loop l_params.put (i + 1, l_infos.item (i).parameter_type) i := i + 1 end end -- Always the type of Current as first argument -- (Eiffel always generates instance methods). l_params.put (0, l_obj.get_type) l_delegate_type := new_delegate_type (l_method_info.return_type, l_params) if l_delegate_type /= Void then Result := {DELEGATE}.create_delegate (l_delegate_type, l_method_info, True) end end end new_delegate_type (a_return_type: SYSTEM_TYPE; a_parameters: NATIVE_ARRAY [SYSTEM_TYPE]): SYSTEM_TYPE local l_name: ASSEMBLY_NAME l_assembly: ASSEMBLY_BUILDER l_module: MODULE_BUILDER l_type: TYPE_BUILDER l_constructor: CONSTRUCTOR_BUILDER l_invoke: METHOD_BUILDER do -- Creating the assembly holding the delegate type create l_name.make ("DelegateDynamicAssembly" + counter.item.out) l_assembly := {APP_DOMAIN}.current_domain.define_dynamic_assembly (l_name, {ASSEMBLY_BUILDER_ACCESS}.run_and_save) l_module := l_assembly.define_dynamic_module (l_name.name, {SYSTEM_STRING}.concat (l_name.name, dll_extension)) -- Creating the delegate type l_type := l_module.define_type ("Delegate" + counter.item.out, {TYPE_ATTRIBUTES}.Public | {TYPE_ATTRIBUTES}.sealed | {TYPE_ATTRIBUTES}.ansi_class | {TYPE_ATTRIBUTES}.auto_class, {MULTICAST_DELEGATE}) -- Creating the .ctor l_constructor := l_type.define_constructor ( {METHOD_ATTRIBUTES}.public | {METHOD_ATTRIBUTES}.special_name | {METHOD_ATTRIBUTES}.rt_special_name | {METHOD_ATTRIBUTES}.hide_by_sig, {CALLING_CONVENTIONS}.standard, << ({SYSTEM_OBJECT}).to_cil, ({POINTER}).to_cil >> ) l_constructor.set_implementation_flags ({METHOD_IMPL_ATTRIBUTES}.runtime | {METHOD_IMPL_ATTRIBUTES}.managed) -- Create `invoke' l_invoke := l_type.define_method ("Invoke", {METHOD_ATTRIBUTES}.public | {METHOD_ATTRIBUTES}.hide_by_sig | {METHOD_ATTRIBUTES}.new_slot | {METHOD_ATTRIBUTES}.virtual, {CALLING_CONVENTIONS}.standard, a_return_type, a_parameters) l_invoke.set_implementation_flags ({METHOD_IMPL_ATTRIBUTES}.runtime | {METHOD_IMPL_ATTRIBUTES}.managed) Result := l_type.create_type l_assembly.save ({SYSTEM_STRING}.concat (l_name.name, dll_extension)) -- Increment our counter counter.put (counter.item + 1) end dll_extension: SYSTEM_STRING = ".dll" -- Extension for assembly/module pascal_case (name: STRING): STRING -- Convert `name' using PascalCasing convention. require name_not_void: name /= Void name_not_empty: not name.is_empty local i, nb: INTEGER l_c: CHARACTER do Result := name Result := Result.twin from i := 2 nb := Result.count Result.put (Result.item (1).upper, 1) until i > nb loop -- When we encounter a '_' we delete it if it is not the last one -- in `Result' and the character following the `_' has its case -- changed to upper. l_c := Result.item (i) if l_c = '_' and i < nb then l_c := Result.item (i + 1) if l_c.upper /= l_c then Result.remove (i) nb := nb - 1 Result.put (l_c.upper, i) end end i := i + 1 end ensure result_not_void: Result /= Void end counter: CELL [INTEGER] once create Result.put (1) end

Comments
  • Peter Gummer (7 years ago 20/1/2010)

    Not type-safe

    Relying on a string to find the routine would have the usual problems of reflection: it would be slow and not type-safe.

    • Manu (7 years ago 20/1/2010)

      Never said it was the ideal solution :-) It is what you can get now without compiler support or changes in the agent classes.

      • Peter Gummer (7 years ago 21/1/2010)

        What about the $ operator?

        I seem to recall using the $ operator to get a new delegate. This would have been several years ago. Is my memory failing me, or has something changed?

        • Manu (7 years ago 22/1/2010)

          The issue I'm trying to resolve in this article is the creation of a proper delegate type and from that type to create an instance of it.

          If you already have a delegate type handy, then indeed you just need to do:

          delegate: DELEGATE_TYPE create delegate.make (Current, $my_routine)
          .