readonly keyword in c sharp

readonly

The readonly keyword is a modifier that you can use on fields. When a field declaration includes a readonly modifier, assignments to the fields introduced by the declaration can only occur as part of the declaration or in a constructor in the same class.

Example

---

In this example, the value of the field year cannot be changed in the method ChangeYear, even though it is assigned a value in the class constructor

class Age

{

    readonly int _year;

    Age(int year)

    {

        _year = year;

    }

    void ChangeYear()

    {

        //_year = 1984; // Compile error if uncommented.

    }

}

You can assign a value to a readonly field only in
the following contexts: 


·        When the variable is initialized in the declaration, for example: 
·         public readonly int s = 52;
·        For an instance field, in the instance

constructors of the class that contains the field declaration. 
he readonly keyword is different from the const keyword. A const field can only be initialized at the declaration of the field. A readonly field can be initialized either at the declaration or in a constructor. Therefore, readonly fields can have different values depending on the constructor used. Also, while a const field is a compile-time constant, the readonly field can be used for runtime constants

: