Note: The read-only variables are useful if we want to have different constant values for the different instances of the class. In the above program, we have reinitialized the read-only variable in the constructor. It displays the following error message. A read-only field cannot be assigned to except in a constructor or a variable initializer. As we already, the readonly variables can be initialized inside the default or parameterized constructor. We can pass readonly variables as ref or out in method parameter if the method is called in the constructor context.
Difference between Ref and Out keywords in C. A mutable type is a type whose instance data can be modified example: StringBuilder. As we know that the read-only modifier prevents the field from being modified by a different instance of the reference type. The ReadOnly does not prevent the instance data of the field from being modified through the reference type.
So, we should not assign read-only to mutable types like collections or arrays because only the reference cannot be changed but the object that holds the values can be changed. In the above example, We can change the values of the ReadOnly list. When we try to assign the list to the new collection, It will throw a compile-time error because only the reference is immutable not the object itself that holds the value.
Browse Articles. Shailendra Chauhan Print 3 min read 14 Nov Constant and ReadOnly keyword is used to make a field constant which value cannot be modified. The static keyword is used to make members static that can be shared by all the class objects. In this article, I am going to explain the difference between these three.
Constant Constant fields or local variables must be assigned a value at the time of declaration and after that, they cannot be modified. By default constant are static, hence you cannot define a constant type as static.
A constant field or local variable can be initialized with a constant expression which must be fully evaluated at compile time. Use the const modifier when you sure that the value a field or local variable would not be changed. ReadOnly A readonly field can be initialized either at the time of declaration or within the constructor of the same class. Therefore, readonly fields can be used for run-time constants. How to combine two arrays without duplicate values in C?
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Declared using the readonly keyword. Declred using the const keyword. Wait before leaving. I am One among a million Software engineers of India. I write beautiful markup. I make the Web useful. Arunkumar Blog Home Posts. Can be accessed through class name Please go through the summary of differences between const and readonly then I will try to explain each point after that.
Table of Contents Const vs Readonly in C : C Const field or local: C ReadOnly Field: Versioning problem of the Const field in C : C Static Readonly field: C Readonly vs Static Readonly: When to use Const and When to use readonly in C Const vs Readonly in C : Const Readonly const keyword can be applied to fields or local variables readonly keyword applies only to fields not local variables We must assign const field at the time of declation only We can assign readonly field at the time of declaration or in constructor,not in any other methods.
No Memory Allocated Because const value embedded in IL code itself after compilation dynamic memory allocated for readonly fields and we can get the value at run time. Const in C are by default static. Can be accessed only through class name Readonly belongs to the object created so accessed through only through instance of class. To make it class member we need to add static keyword before readonly. Same as Const The value is constant as it is belongs to class The value may be different depending upon constructor used as it belongs to object of the class If we want to declare const for someclass non-primitive types we should assign it to null which as of no use.
If you declare a non-primitive types reference type as readonly only reference is immutable not the object it contains. Readonly in C Static Readonly in C Can be assigned at the time of declaration or constructor Can be assigned at the time of declaration or static constructor Value may be different depending upon the constructor used Value will be constant after the initialization.
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