C# Class Microsoft.Scripting.ComInterop.IDispatchComObject

An object that implements IDispatch This currently has the following issues: 1. If we prefer ComObjectWithTypeInfo over IDispatchComObject, then we will often not IDispatchComObject since implementations of IDispatch often rely on a registered type library. If we prefer IDispatchComObject over ComObjectWithTypeInfo, users get a non-ideal experience. 2. IDispatch cannot distinguish between properties and methods with 0 arguments (and non-0 default arguments?). So obj.foo() is ambiguous as it could mean invoking method foo, or it could mean invoking the function pointer returned by property foo. We are attempting to find whether we need to call a method or a property by examining the ITypeInfo associated with the IDispatch. ITypeInfo tell's use what parameters the method expects, is it a method or a property, what is the default property of the object, how to create an enumerator for collections etc. 3. IronPython processes the signature and converts ref arguments into return values. However, since the signature of a DispMethod is not available beforehand, this conversion is not possible. There could be other signature conversions that may be affected. How does VB6 deal with ref arguments and IDispatch? We also support events for IDispatch objects: Background: COM objects support events through a mechanism known as Connect Points. Connection Points are separate objects created off the actual COM object (this is to prevent circular references between event sink and event source). When clients want to sink events generated by COM object they would implement callback interfaces (aka source interfaces) and hand it over (advise) to the Connection Point. Implementation details: When IDispatchComObject.TryGetMember request is received we first check whether the requested member is a property or a method. If this check fails we will try to determine whether an event is requested. To do so we will do the following set of steps: 1. Verify the COM object implements IConnectionPointContainer 2. Attempt to find COM object's coclass's description a. Query the object for IProvideClassInfo interface. Go to 3, if found b. From object's IDispatch retrieve primary interface description c. Scan coclasses declared in object's type library. d. Find coclass implementing this particular primary interface 3. Scan coclass for all its source interfaces. 4. Check whether to any of the methods on the source interfaces matches the request name Once we determine that TryGetMember requests an event we will return an instance of BoundDispEvent class. This class has InPlaceAdd and InPlaceSubtract operators defined. Calling InPlaceAdd operator will: 1. An instance of ComEventSinksContainer class is created (unless RCW already had one). This instance is hanged off the RCW in attempt to bind the lifetime of event sinks to the lifetime of the RCW itself, meaning event sink will be collected once the RCW is collected (this is the same way event sinks lifetime is controlled by PIAs). Notice: ComEventSinksContainer contains a Finalizer which will go and unadvise all event sinks. Notice: ComEventSinksContainer is a list of ComEventSink objects. 2. Unless we have already created a ComEventSink for the required source interface, we will create and advise a new ComEventSink. Each ComEventSink implements a single source interface that COM object supports. 3. ComEventSink contains a map between method DISPIDs to the multicast delegate that will be invoked when the event is raised. 4. ComEventSink implements IReflect interface which is exposed as custom IDispatch to COM consumers. This allows us to intercept calls to IDispatch.Invoke and apply custom logic - in particular we will just find and invoke the multicast delegate corresponding to the invoked dispid.