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Showing posts from 2008

Casting Restrictions ???

We all know that the runtime can detect the actual type of a System.Object instance. The primitive data types provided by the runtime are compatible with one another for casting (assuming that we do not truncate the values). So if I have an int, it can be cast to long or ulong. All that is fine. Watch this:-
interface IAppDataTypeBase { // Other methods GetValue(); } Since IAppDataTypeBase represents the mother of all types of data in my application, I have made GetValue to return the value as object (I could have used generics, that is for another day!).
IAppDataTypeBase longType = GetLongInstanceFromSomeWhere(); int i = (int)longType.GetValue();So are we discussing any problems here? Yes, we are. The problem is that the value returned by GetValue - System.Object - despite being inherently long cannot be cast to an int. It would result in an 'Specified cast is invalid' exception. If an object is one of the primitive types, it can only be cast to its actual type. In the ab…

Understanding (ref)erences !!!

Let us take a look at the following piece of code:- public void Operate(IList iList2)
{
iList2 = new List();
iList2.Add(1);
iList2.Add(2);
iList2.Add(3);
}

public static void Main()
{
IList iList= new List();
iList.Add(10);
Operate(iList);
Console.WriteLine(iList[0].ToString());
}Be thinking about what would the above program print to the console ? And that is what we are going to talk about in this post - simple but subtle.
I saw this code at CodeProject discussions. The author was confused with why was the program printing 10 instead of 1. I am writing about this since the 'gotcha' was not highlighted in the discussion.
So we passed the reference 'iList' to the function which is supposed to make it point to the 'List' that it creates and so must be printing 1. Well, a C++ programmer knowing how to program in C# would have said 'Gotcha' already. A reference (in C#), equivalent to a pointer in C++, is an entity that stores the address of an object in heap and a…

Extension Methods - A Polished C++ Feature !!!

Extension Method is an excellent feature in C# 3.0. It is a mechanism by which new methods can be exposed from an existing type (interface or class) without directly adding the method to the type. Why do we need extension methods anyway ? Ok, that is the big story of lamba and LINQ. But from a conceptual standpoint, the extension methods establish a mechanism to extend the public interface of a type. The compiler is smart enough to make the method a part of the public interface of the type. Yeah, that is what it does, and the intellisense is very cool in making us believe that. It is cleaner and easier (for the library developers and for us programmers even) to add extra functionality (methods) not provided in the type. That is the intent. And we know that was exercised extravagantly in LINQ. The IEnumerable was extended with a whole lot set of methods to aid the LINQ design. Remember the Where, Select etc methods on IEnumerable. An example code snippet is worth a thousand …