Skip to main content

Missing MI !!!

We all know C# does not offer multiple inheritance but offers arguments that programmers can live without it. It is true in almost all cases, especially all cat and animal or employee and manager projects. I have seen a few cases where if C# offered multiple inheritance, the solution would have been natural, elegant and succinct.

Imagine that I have a component (UI, non-UI, doesn't matter). You can make calls into the component, which does some interesting work for you. Imagine that the component takes an interface IComponentCallback to notify its parent. So I would do is have my parent class derive from IComponentCallback interface and pass this to the component. The code would look something like this:-

interface IComponentCallback
   void Callback1();
   bool Callback2();
   void Callback3(int old, int new);

class SomeComponent
   // The parent on whom callbacks are made
   private IComponentCallback _parent = null;
   public SomeCompoent(IComponentCallback cmpCallback)
      // Imagine that callbacks would not be made      
      // if cmpCallback is null
      _parent = cmpCallback;
   // Other methods in which _parent shall be used
   // for making the callbacks.

class Parent : IComponentCallback
   private SomeComponent _someComponent = null;
   public Parent()
      _someComponent = new SomeComponent(this as IComponentCallback);
   #region IComponentCallback methods implementation
   void IComponentCallback.Callback1()
      // Code making use of this callback
   bool IComponentCallback.Callback2()
      // Possible code to provide some    
      return true;
   void Callback3(int old, int new)
      // Code making use of old\new

void Main(string[] args)
   // .... code ...
   // Instantiating a parent which would create 
   // SomeComponent and establish itself as the
   // callback sink.
   Parent p = new Parent();
   // ... Code ...

This is a typical case where the instantiator is the callback sink. And this case is natural and usual. There may be cases where one class instantiates and holds the component while a different class acts as the callback sink. That... is not the topic of our discussion.

Now imagine our parent is a Form class. I am sure you might have come across this case where a Form hosts a UI or non-UI component and you want the callback sink as methods in your class so that you can update the UI directly. What follows may necessarily be the common case but I encountered it more than a few times. In our application, any parent could host the component. There were certain things common to do when processing the callback and hence we wrote a (base) class implementing IComponentCallback and which represents the component callback sink. Since C# does not support MI, any of our custom forms could not be derived from the callback sink class, since they are already derived from System.Windows.Form class.

Now it is not wise to argue that one may use delegates or that this implementation is bad or this is a corner case. I have practically encountered this a few times where the component we are talking about is from a third party. In some cases, the component was our own and implemented for callback mechanism, called plugin, whose intent is quite opposite to event notification. Most others might have "No MI in C#" in mind and would have the sink class as a member of the Form (parent). I don't see that natural but compulsion.

Anyways, a case exists, and of course you can live without MI.


Popular posts from this blog

Passing CComPtr By Value !!!

This is about a killer bug identified by our chief software engineer in our software. What was devised for ease of use and write smart code ended up in this killer defect due to improper perception. Ok, let us go!CComPtr is a template class in ATL designed to wrap the discrete functionality of COM object management - AddRef and Release. Technically it is a smart pointer for a COM object.void SomeMethod() { CComPtr siPtr; HRESULT hr = siPtr.CoCreateInstance(CLSID_SomeComponent); siPtr->MethodOne(20, L"Hello"); }Without CComPtr, the code wouldn't be as elegant as above. The code would be spilled with AddRef and Release. Besides, writing code to Release after use under any circumstance is either hard or ugly. CComPtr automatically takes care of releasing in its destructor just like std::auto_ptr. As a C++ programmer, we must be able to appreciate the inevitability of the destructor and its immense use in writing smart code. However there is a difference between …

jqGrid: Handling array data !!!

This post is primarily a personal reference. I also consider this a tribute to Oleg, who was fundamental in improving my understanding of the jqGrid internals - the way it handles source data types, which if I may say led him in discovering a bug in jqGrid.

If you are working with local array data as the source for jqGrid, meaning you will get the data from the server but want the jqGrid not to talk to the server anymore, and want to have custom handling of the edit functionality/form and delete functionality, it is not going to be straightforward - you need to have a decent understanding of how jqGrid works, and you should be aware of the bug Oleg pointed in our discussion. I repeat this is all about using jqGrid to manage array data locally, no posting to server when you edit or delete, which is where the bug is.

$('#grid').jqGrid('navGrid', '#pager', { recreateForm: true, add: false, search: false, refresh: false, …

Offering __FILE__ and __LINE__ for C# !!!

Not the same way but we could say better.
Visual Studio 2012, another power packed release of Visual Studio, among a lot of other powerful fancy language features, offers the ability to deduce the method caller details at compile time.
C++ offered the compiler defined macros __FILE__ and __LINE__ (and __DATE__ and __TIME__), which are primarily intended for diagnostic purposes in a program, whereby the caller information is captured and logged. For instance, using __LINE__ would be replaced with the exact line number in the file where this macro has been used. That sometimes beats the purpose and doesn't gives us what we actually expect. Let's see.

For instance, suppose you wish to write a verbose Log method with an idea to print rich diagnostic details, it would look something like this.
void LogException(const std::string& logText, const std::string& fileName, …