UnCommon C# keywords - A Look
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CONTENTS
This is really a weird topic to start with. But still I would like to give you an insight on some of the uncommon things that you may not have noticed while doing programming. I have framed them in 2 sections.
1st one for Undocumented Keywords, which you will not find anywhere, not even in MSDN Documentation, which are not listed to intellesense menu in visual studio.
2nd one for Documented Keywords which are uncommon or just being introduced to C#. Documented keywords which are uncommon can be found over MSDN.
I have also made a sample application where I have given some demonstration of each of the topics mentioned here in this article. If you want to test these, please download the sample application from here :
Download UncommonTestSample_V3.zip - 121.34 KB
Undocumented Keywords
Let us discuss some of the undocumented keywords that I found. If you know any keyword other than this please let me know :
1. __arglist
Lets start with __arglist
. __arglist
is used to send parameters to a method. Generally we used to send parameters to a function by having a list of arguments specified in the method head. If we want to pass a new set of arguments we need to have Method Overloading. Even when we want to send any number of arguments we might use param array.
Now why should we use __arglist
. In case of each of these methods, the problems are :
1. If we use Method Overloading, we might have to add new methods whenever a new set of argument list is thought to be sent.
2. If we use param array we need to have same type of arguments or need to have param array of objects.
__arglist
reveals each of those. It can send any no of argument to a function. It might be of any type and we can parse each argument easily using simple steps.
Lets have a look at the Code :
![](http://www.codeproject.com/images/minus.gif)
public int paramLength(__arglist)
{
ArgIterator iterator = new ArgIterator(__arglist);
return iterator.GetRemainingCount();
}
Now if I call the function using this statement
![](http://www.codeproject.com/images/minus.gif)
int x = this.paramLength(__arglist(49,34,54,6,"Manimoy")); // returns 5
5 will be returned to the variable x. It is because we send 5 arguments to the method. We can access each methods using :
![](http://www.codeproject.com/images/minus.gif)
TypedReference tf = iterator.GetNextArg();
TypedReference.ToObject(tf)
On each call to GetNextArg
, the GetRemainingCount
will decrease by one until it wipes out each objects set to the iterator.
2. __refvalue
Another interesting keyword you can use instead is __refvalue
. It is used to fetch the value from a reference object. You can use this to get the actual object from TypedReference
object.
It takes 2 arguments, first one is the object of TypedReference
and the Type in which to cast. Take a look on the line below :
![](http://www.codeproject.com/images/minus.gif)
int tfValue = __refvalue(tf, int);
On the execution of the line tfValue
will be assigned to the value of the integer where tf is pointing.
3. __makeref
Another undocumented keyword is __makeref
which will give the TypedReference
object from the object itself. This is just the reverse to __refvalue
. Take a look at the code below :
![](http://www.codeproject.com/images/minus.gif)
string name = "Ayan";
TypedReference tf = __makeref(name);
4. __reftype
__reftype
is used to get Type
object from a TypedReference
. Have a look at the code below to understand the use :
![](http://www.codeproject.com/images/minus.gif)
Type t = __reftype(tf);
if(t.ToString().equals("System.String"))
string str = __refvalue(t,string);
Note : Though I found these keywords in all the versions of C#, yet I dont use it in production environment. There is no sureity of these keywords to be there in future version of C#, so use it in your own risk.
Documented Yet Uncommon
In this section, I am going to discuss some of the uncommon documented keywords which is not needed very often while we do programs. Let us discuss the most common one here in this section.
1. Yield
Yield
is a keyword introduced in .NET 2.0, is used to yield a list of return statements in the form of IEnumerable
. The block which yields
is commonly called as iterator block. In the code below, I have created a list of few names and returned the list of all of them which has length less than 5 until it reaches IEnumerable
yield break
statement for a length >12
![](http://www.codeproject.com/images/minus.gif)
List<string> lst = new List<string>();
lst.Add("Abhishek");
lst.Add("Abhijit");
lst.Add("Manimoy");
lst.Add("Raj");
lst.Add("Ayan");
lst.Add("MacMillanRojer");
lst.Add("Rizzuto");
foreach (string x in lst)
{
if (x.Length > 12) // Breaks on MacMillanRojer
yield break;
else if (x.Length > 5) // Only returns those which are having length >5
yield return x;
else continue;
}
Actually the yield return x
will evaluate each elements and creates the
of all the elements that satisfies the condition(length>5).enumerable
The break
statement will terminate the loop and return the existing Enumerable
created.
2. Fixed
Another uncommon keyword is Fixed which can only be used in Unsafe
C# code blocks. Fixed
statement sets the pointer to be in a fixed memory address so that, it will not be moved to anywhere even if Garbage Collection Thread is invoked. Let us have a look at the code below:
![](http://www.codeproject.com/images/minus.gif)
int[] a = new int[] { 1, 2, 3 };
fixed (int* pt = a)
{
int* c = pt;
MessageBox.Show("Value : " + *c);
// This will fix the variable totally so that it will
// not be moved when Garbage collector is invoked.
}
Here, the Pointer c is be assigned the same location as pt.
Fixed often comes at a cost. It is actually hampers the normal process of Garbage collection. Thus if is good to avoid fixed statement if not actually needed.
3 Checked / Unchecked
Another keyword called checked
which is used to control arithmetic overflow context. Checked keyword throws OverflowException
when an arithmetic operation overflows the necessary size.
Take a look at the code :
![](http://www.codeproject.com/images/minus.gif)
int x = int.MaxValue;
int y = int.MaxValue;
int z = checked(x + y);
The above statement throws OverflowException
when x+y is invoked. The checked
is used to check the overflow in arithmetic calculations and throw exception accordingly. z is assinged to 0 when OverflowException
occurs.
We might use unchecked
keyword when we dont need to throw exception.
![](http://www.codeproject.com/images/minus.gif)
int x = int.MaxValue;
int y = int.MaxValue;
int z = unchecked(x + y);
Through execution of above code the value of z will be assigned to -2.
4. Volatile
Volatile
keyword is used to define a variable which is to be modified across multiple threads
without invoking lock
statements(Although we do lock them most of the times). Volatile variables are not subject to compiler optimization and thus we will get the most updated value of the variable all the time. See the example below :
![](http://www.codeproject.com/images/minus.gif)
public volatile int i;
Thread th = new Thread(new ThreadStart(VolatileInvoke));
th.Start();
Thread.Sleep(5000); //Holds current Thread for 5 seconds.
MessageBox.Show("Value of i : " + i);
th.Abort();
private void VolatileInvoke()
{
while (true)
{
i++;
}
}
The thread is started and will increment the volatile integer value by 1 until it is aborted by the main thread.
Note : Volatile
types dont have Thread optimization.
5. StackAlloc
It is also used with unsafe
C# code which allocates memory dynamically from stack. stackalloc
is used to acquire memory quickly when it is very essential memory quickly. We can use the advantage of Fast accessible memory when we use it from Stack. We can declare an array like this :
![](http://www.codeproject.com/images/minus.gif)
int* array = stackalloc new int[1000]
The memory is available as soon as the statement is invoked.
Note: You should always keep in mind, stackalloc
memory is very limited. It is by default 1MB for each thread. So if we need huge amount of memory(more than 1MB) we have to rely back to our original Heap memory structure.
6. Global ::
It is very handy when local namespace hides global namespace. Suppose we have created a class named System in our project. C# allowes to do that. But the problem is that whenever I want to call System
that is defined in the global space, we unable to do that without using global::
. Let us see the example below :
![](http://www.codeproject.com/images/minus.gif)
internal class System
{
internal class Array :IEnumerable
{
public int Length
{
get{return 1000}
}
#region IEnumerable Members
public IEnumerator GetEnumerator()
{
Debug.Write("This is Dummy Array");
return base.GetEnumerator();
}
#endregion
}
}
Now if you want to call System.Array
it will call the one defined locally. To call global System we need to use global::System
It is always better to use global::
when you are sure of calling the global namespace. This ensures your code to work even in this sort of weird situations.
7. Namespace/Class Alias
We use using to define Alias. There are 2 types of Alias:
1. Namespace Alias:
Namespace alias are used when you want to shorten a long namespace. To do that :
![](http://www.codeproject.com/images/minus.gif)
using Abhishek = System.Drawing;
public class X
{
public X()
{
Abhishek.Graphics g = this.CreateGraphics();
}
}
Here in the header we made an alias Abhishek
of System.Drawing
. Thus within the code if we refer to Abhishek
, it will be same as referring to System.Drawing
.
Class Alias:
You can also make use of using
statement to define reference to a single class. Say if I write using Abhishek=System.Drawing.Bitmap;
Abhisek will hold the class Bitmap
. We can create Object of Abhishek
, access static functions directly.
![](http://www.codeproject.com/images/minus.gif)
using Abhishek=System.Drawing.Graphics;
public class X
{
public X()
{
Abhishek g = this.CreateGraphics();
}
}
Thus Abhishek
will be pointing to native Graphics
object rather than the entire namespace
.
8. extern alias
Most of us while working with C# have used external control sets. There may come a situation when we want to add 2 versions of dlls in the same application with same Fully Qualified Namespaces. In such cases we need extern alias feature to refer to two different assemblies.
For example:
Suppose we add an assembly x10.dll (V1)
which have a class called Y.
We add x20.dll(V2)
where we may want to use Class Y.
First of all, to reference the fully qualified assembly we need to declare an alias in command line.
/r:XV1=X10.dll
/r:XV2=X20.dll
Now to reference that we use
![](http://www.codeproject.com/images/minus.gif)
extern alias XV1;
extern alias XV2;
9. ?? (Null coalescing operator)
Null coalescing operator is used to work with null values. It is introduced in 2.0. See the following :
![](http://www.codeproject.com/images/minus.gif)
MyClass x = null;
x = x ?? new MyClass();
?? means if x has null value it will call new MyClass
() otherwise it will assign the existing x.
10. @variables
Generally C# doesn't allow to create variables in the same name as keywords. But there is a way out to this. We can define variable with same name as keywords using @.
Suppose we define
int @int = 10;
That means a variable with name int is declared and assigned a value 10 in it.
11. Readonly
readonly
is a keyword present in C# which is used to create variables that will not change throughout the program. The variable declared as readonly
will be assigned its value only once and it will remain the same value throughout the execution of the object.
To declare a variable as readonly
:
![](http://www.codeproject.com/images/minus.gif)
public readonly int readonlyvariable = 20;
This will instruct the program to make the variable 20 and any further re-assign to the variable is not permitted.
12 Difference between Const & readonly ?
readonly
is almost similar to const
keyword. The only difference is that const
variables are defined in compile time, while readonly
variables are defined at runtime during object initialization. You can assign readonly
variables from within constructors, so based on the constructor call you may assign readonly values differently.
![](http://www.codeproject.com/images/minus.gif)
public readonly int readsecond;
public Documented()
{
readsecond = DateTime.Now.Second;
}
Here the readsecond
will assign values differently based on the object initialization, which is impossible in case of const
.
13 Default
Sometimes default
keywords comes very handy when working with generic objects. It returns the default value when the object is not initialized. For example, we all know integers are initialized to 0 if not given any value. Characters are Empty when not given any value, objects are null when not assigned any value.
These values are assigned based on default
keyword.
Thus if we write :
![](http://www.codeproject.com/images/minus.gif)
int x = default(int);//will be assigned to 0
will be same as int x;
In case of Generic object when the type is undefined, we can use default to assign specific value to the object. Let us look at the sample :
![](http://www.codeproject.com/images/minus.gif)
public T GetDefault<T>()
{
return default(T);
}
The function returns default value for each individual types sent. Thus
![](http://www.codeproject.com/images/minus.gif)
int defx = this.GetDefault<int>(); //will assign 0
char defy = this.GetDefault<char>(); // will assign null('\0')
object defz = this.GetDefault<object>(); // will assign null
Thus we can use default
keyword to get the default assignments to the object very easily.
14. Nullable Types
Nullable
types of C# can handle nulls even being primitive data types. Each nullable types are derived from System.Nullable
. We can define nullables like this :
![](http://www.codeproject.com/images/minus.gif)
int? nullableint = null;
Thus nullableint
will be assigned to
. null
If you access nullable variables, you will get 2 properties.
HasValue
which returns false
if null is assigned to the variable, and Value
which returns the actual value of the variable. You can also use GetValueOrDefault
function of each nullable type object to get the default value when null is assigned to the variable.
Conclusion
This concludes most of the keywords. My intention is to give you a brief knowledge about them and how to use them. Please feel free to comment.
You can try out the sample application from here
- Download UncommonTestSample_V3.zip - 127.01 KB(LATEST)
- Download UncommonTestSample_V2.zip - 121.34 KB
- Download UncommonTestSample.zip - 59.08 KB
Hope you like this article. For further reference you can read MSDN
http://www.codeproject.com/Articles/38695/UnCommon-Csharp-keywords-A-Look.aspx