Optional and Named parameters in C# 4.0

C# 4.0 and ASP.NET 4.0 are part of .NET 4.0. Visual Studio.NET 2010 supports .Net 4.0 and it is in its beta 1 as of now.  In order to try new features of C# 4.0, you need to install VS2010, which can be downloaded from Visual Studio Website.

The major addition to C# 4.0 are:

• Optional and named parameters
• Dynamic Lookup
• Variance - Covariance and Contravariance

Optional Parameters

static void Fun(int x, int y = 20, int z = 30)
{
    Console.WriteLine("{0},{1},{2}", x, y, z);
}

Fun(10);        // y and z default to 20 and 30
Fun(1, 2, 3);   //  passing all three parameters
Fun(100, 200);  // x = 100, y = 200 and z defaults to 30

static void Fun(int x = 10, int y, int z)  // cannot have mandatory parameters after optional parameter
{
    // code
}

Named parameters

Fun(100, z: 300);  // 100 is passed to x and 300 to z

Parametername : value

static void Print(int x, int y)
{        
   Console.WriteLine("Values are {0}, {1}", x, y);
}

Print(y: 10, x: 20);        

static void Search(string sentence, string word, int spos = 0, int occurrence = 1)
{
      // code
}

 pos = Search("How do you do", "do");
 // start search from 5th position
 pos = Search("How do you do", "do",5); 
 // start search from 0th position(taken by default) but look for 2nd occurrence. 
 pos = Search("How do you do", "do", occurrence:2); 

Srikanth

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