"Read Only" Fields | "Ref" Parameter's | "Out" Parameter's | "this" Keywords | "Named" Parameter's

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ReadOnly Fields :

1. The ReadOnly members are just like constants according to the objects.
2. The Readonly modifier can be used for fields only.
3. Once you initialize the value of ReadOnly data members, the object can‘t change that value, but it can access the value.
4. Note : The read only field‘s values can be changed inside of the class only.
5. To declare the read only fields:
   Syntax : access_specifier readonly data_type variable_name = value;

C# Coding on ReadOnly Fields :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ReadOnlyDataMembersDemo
{
 class Sample
 {
  //read only data member
   public readonly string CompanyName = "Software IT Technologies";
 }
 class Program
  {
   static void Main(string[] args)
    {
     Sample s = new Sample();
     Console.WriteLine(s.CompanyName);
     //s.CompanyName = "TCS"; // is not allowed bcoz it is the readonly member.
     Console.Read();
    }
  }
} 

Ref Parameters :

• The reference parameters are similar to the normal parameters.
• The only difference between the normal parameters and reference parameters is: When the value is changed in the reference parameter, would automatically affect the actual parameter in the calling portion.
• Implementation: Use "ref" keyword in calling portion and also in method definition.
• Rule : The actual parameter at the calling portion should be a variable and can‘t be a constant.
• This is just like Call by reference concept in C/C++.

C# Coding on Ref Parameters :

namespace RefParameterDemo
 {
  class SampleClass
  {
   public void FirstMethod(int x, int y)
   {
    x++;
    y++;
   }
   public void SecondMethod(int x, ref int y)
   {
    x++;
    y++;
   }
  }

class Program
 {
  static void Main(string[] args)
  {
   int a = 10, b = 20;
   SampleClass sc = new SampleClass();
   Console.WriteLine(a + ", " + b);
   sc.FirstMethod(a, b);
   Console.WriteLine(a + ", " + b);
   sc.SecondMethod(a, ref b);
   Console.WriteLine(a + ", " + b);
   Console.Read();
  }
 }
} 

OUT Parameters :

1. This is to return multiple values from a method.
2. The "out" parameter is similar to "ref" parameter; but the difference between these two parameters is, "out" parameter does not carries any value from calling portion to the method definition; but it carries the return value to the calling portion.
3. Implementation : Use "out" keyword in calling portion and also in method definition.
4. So, the "out" may not be initialized, when you call the method.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace OutParametersDemo
{
 class Test
 {
  public string GetBigAndSmall(string s1, string s2, out string small)
  {
   string big;
   if (s1.Length > s2.Length)
    big = s1;
   else
    big = s2;
   if (s1.Length < s2.Length)
    small = s1;
   else
    small = s2;
   return (big);
  }
 }

 class Program
 {
  static void Main(string[] args)
  {
   Test t = new Test();
   string s1 = "dotnet";
   string s2 = "framework";
   string small; //no need of initialization
   string big;
   big = t.GetBigAndSmall(s1, s2, out small);
   Console.WriteLine("Small string: " + small);
   Console.WriteLine("Big string: " + big);
   Console.Read();
  }
 }
}

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