Using Deconstructors in C# 7.0

This is another awesome feature that got introduced with C# 7.0 which can be helpful in many scenarios while consuming various objects. Deconstruction is mostly discussed with another new feature System.ValueTuple but it can be used with other custom type as well. I have also discussed it in briefly in ValueTuple post at the link below. I will advise to go through that first before starting here.

How to use the new ValueTuples : A C# 7.0 feature

What is Deconstruction

It is a process of splitting an instance’s (value types and reference types) value into multiple parts and assigning them to new variables. Like, I mentioned that it is extremely useful with the Tuples which contains a set of values but can be used with other types.

How to use Deconstruction

We can leverage it in our custom classes, structs or interfaces. We need to implement Deconstruct method, which returns void and each deconstructed value should be added as out parameter in the method signature. We can have multiple overridden Deconstruct method based on the requirement. Let’s see an example

public class Person
{
    public string FirstName { get; set; }

    public string MiddleName { get; set; }

    public string LastName { get; set; }

    public int Age { get; set; }

    public Person(string fName, string mName, string lName, int age)
    {
        FirstName = fName;
        MiddleName = mName;
        LastName = lName;
        Age = age;
    }
    public void Deconstruct(out string fName, out string lName)
    {
        fName = FirstName;
        lName = LastName;
    }

    public void Deconstruct(out string fName, out string lName, out int age)
    {
        fName = FirstName;
        lName = LastName;
        age = Age;
    }
}

Here we can see that I have provided two Deconstruct methods, one with two out parameters: fName, lName and other with three : fName, lName, age.

Person p = new Person("Brij", "Bhushan", "Mishra", 32);

//(string firstName, string lastName) = p;
// OR
var (firstName, lastName) = p;

Console.WriteLine($"Person Details: First Name: {firstName}, Last Name: {lastName}");


(string firstName, string lastName, int age) = p;

Console.WriteLine($"Person Details: First Name: {firstName}, Last Name: {lastName}, Age: {age}");

Here I created the instance of Person with all the details. Then in first deconstruction, we got the first name and last name which calls the first Deconstruct method of the class which has two out parameters. Note that we have two ways of deconstruction. First we explicitly declare the type of each field inside parentheses (commented out) and another, using var keyword so that C# infers the type of each variable. Similarly later, second Deconstruct method is called which deconstructs it in three variables. It can be really useful when we have a class with numerous properties, fields and most of the time, we need only few there we can use the Deconstruct methods.

Similar to ValueTuples, we can use discards here as well. To discard a variable of Deconstruct method, we can use underscore (_) as

Person p = new Person("Brij", "Bhushan", "Mishra", 32);
(string firstName, _ , int age) = p;

Console.WriteLine($"Hello {firstName}, your age is {age}");

Deconstruction use Extension method

There could be scenarios where you want to this feature but its an existing class where changes are not possible (like some third party classes, classes own by different team or even framework classes), there we can add this as an extension method. Lets assume that Person class doesn’t have Deconstruct methods and we can add it as an extension method as

public static class DeconstructionExtensions
{
    public static void Deconstruct( this Person p, out string fName, out string lName, out int age)
    {
        fName = p.FirstName;
        lName = p.LastName;
        age = p.Age;
    }
}

It will work in the same way as earlier.

Hope you have enjoyed the post and will be able to use in your day to day coding.

Thanks
Brij

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Ref and Out improvements in C# 7.0

If you have been observing last few releases of C#, the key focus of C# language team is to improve the developer productivity by reducing the repetitive/common code and performance of the application. First one, helps a lot in writing cleaner and concise code so it mainly contains logic instead of number of lines for null check etc.

ref and out keywords are available with C# since long and very useful in many scenarios. These were serving the purpose quite beautifully but there were few improvements in C# 7.0 which makes it more attractive. In this post, I am not going to discuss the basics of these keywords detail but mainly focus on the improvements in C# 7.0.

Ref keyword – This keyword is used to pass the parameter by reference (even if it is value type) to a method. When we pass the parameter by reference, any change that takes place in the called method also reflects in calling method. ref keyword should be used by in calling method while passing the parameter and in the called method as well. Also unassigned variable cannot be passed as well. Lets see a quick example

static void Main(string[] args)
{
    Point p;
    p.x = 10;
    p.y = 20;

    UpdateCoordinates(ref p);

    Console.WriteLine($"Point coordinates x : {p.x}, y : {p.y}"); // Output: Point coordinates x : 20, y : 40

    Console.ReadKey();
}

static void UpdateCoordinates(ref Point p)
{
    p.x = 20;
    p.y = 40;
}

public struct Point
{
    public int x, y;
}

Here Point is a value type and it is passed using ref keyword. Here the variable gets updated in the called method and it shows 20 and 40 in output.

Note: ref keyword can be used with reference types as well. You can refer one of my previous posts for details here 

C# 7.0 Enhancements :

As in the example above, the values are passed by reference in the method but what about returning the values by reference. For this, there were two enhancements introduced

1- Ref Returns : For this, we need to add ref keyword after return statement in a method and before the return type in the method signature. This feature can be used only in Class (not structs). Let see the Point class as

public class Point
{
    private int x, y;

    public Point(int a, int b)
    {
        this.x = a;
        this.y = b;
    }
    public ref int GetX()
    {
        return ref this.x;
    }

    public ref int GetY()
    {
        return ref this.y;
    }
      
    public void Display()
    {
        Console.WriteLine($"Point coordinates x : {x}, y : {y}");
    }
}

Here I added two methods GetX and GetY which returns x and y by reference. ref keyword also got added with method signature as well.

2- Ref Locals: To store a reference variable (ref), returned by a method, the local variable should also be added with ref keyword before the type and adding the ref keyword before the method call. Now the local variable contains the value by reference and has the ability to change the value of variable which will reflect in the original variable as well. We can call the method without using the ref keyword which will behave as normal method call and the returned value will be a copy of the value.

static void Main(string[] args)
{
    Point p = new Point(10, 20);

    ref int i = ref p.GetX();
    i = 50;

    p.Display(); // Output: Point coordinates x : 50, y : 20

    int j = p.GetY();
    j = 100;

    p.Display(); // Output: Point coordinates x : 50, y : 20

    Console.ReadKey();
}

Initially the values of x and y are 10 and 20. We got the variable x by refernce and updated it to 50 using variable i which is reflected in output. We also received the value of y without using ref which creates a copy of the variable and updating it doesn’t affect the instance p.

It is a really nice feature in scenarios where the values are required to be updated at different places. This also can be when we have a collection of values and few of the items can be updated by the caller method based on the need.

Enhancements in Out parameter: There is a small enhancements in out parameter usage. Earlier out parameter is used as

static void Main(string[] args)
{
    int age;
    string name = GetUserDetails(out age);
    Console.WriteLine($"name : {name}, age : {age}");

    Console.ReadKey();
}

public static string GetUserDetails(out int age)
{
    age = 32;
    return "Brij";
}

Now after enhancement, we dont need to declare the variable first, instead we can direcly declare in the paarmeter as well as

static void Main(string[] args)
{
    //int age;
    string name = GetUserDetails(out int age);
    Console.WriteLine($"name : {name}, age : {age}");

    Console.ReadKey();
}

Although this is a small enhancement but makes more sense.

Hope you enjoyed the post and will be able leverage these enhancements in your day to day coding.

Cheers,
Brij

How to use the new ValueTuples : A C# 7.0 feature

Tuples are one of the awesome features of C# which was initially introduced with .NET 4.0. Although it is less used but it become very handy when we need to return multiple values from a function. We have another option to use out operator but it is not recommended due to various reasons. I am not going to discuss it in this post. Tuple is a static class under namespace System which implements a Factory pattern to create the instances of Tuples. It has a Create method with eight overloads which allows us to have 8 elements in a Tuple. Also, we can have nested tuples as well.

There were few issues with System.Tuple. It is a reference type so even if you are returning few values type elements , the instance gets created on heap, means adding pressure on Garbage Collector. It doesn’t allow to provide a name to the elements, instead we have to refer it as item1, item2.. etc. Also, the way we used to create Tuple is also quite verbose.

Tuple in C# 7.0

C# 7.0 introduces System.ValueTuple as a new language feature, which resolves the problems mentioned above and provides few more additional features. And Yes, it has the power of Value Type so it removes the GC overhead of the old tuple.

Note: ValueTuple is available as indepedent nuget package. You can install it from here.

Lets see few examples of new Value Tuples,

Tuple Literals

Tuple literal is a comma separated list of literal (of various types), surrounded by parenthesis.

static void Main(string[] args)
{
    // Tuple Literals
    var tpl = (1, 2);
    var author = ("Brij", 32, "https://codewala.net/");
}

public (string, int, string) Author { get; set; } = ("Brij", 32, "https://codewala.net/");

Here we can see that creating Tuple is now a simple assignment operation. Also we can have different types in a Tuple which helps in combining various set of information in a tuple based on the need.

Using Tuples as Return Type

We can use value tuple as return type and the syntax looks so simple as


var author = GetAuthor();

Console.WriteLine($"Author Details: Name: {author.Item1}, Age: {author.Item2}, BlogURL : {author.Item3 ?? "URL not available" } ");

private static (string, int, string) GetAuthor()
{
    string name = "Amit Kumar";
    int age = 33;
    return (name, age, null);
}

Naming the Tuple Elements:
Yes, we can name the tuple elements and this also provides the intellisense support. This is one of the best improvements. We can write the above code as

var author = GetAuthor();
WriteLine($"Author Details: Name: {author.name}, Age: {author.age}, BlogURL : {author.url ?? "URL not available" } ");

private static (string name, int age, string url) GetAuthor()
{
    string name = "Amit Kumar";
    int age = 33;
    return (name, age, null);
}

We can give names in tuple literal as well

var author = (name: "Brij", age: 32, url: "https://codewala.net/");      
Console.WriteLine($"Author Details: Name: {author.name}, Age: {author.age}, BlogURL : {author.url ?? "URL not available" } ");
// Or we can also write as
(string name, int age, string url) author = ("Brij", 32, "https://codewala.net/");

Let’s move to another exciting feature

Value Tuple Deconstruction

Value tuple allows us deconstruct the tuple and access the elements as a local variable. We need to assign a tuple to variable surrounded by parenthesis.  Broadly, it can be done in three ways

  • Providing the types of each element in parenthesis.
  • Using var keyword outside the parenthesis (it is applied to each variable).
  • Or using existing variables

Lets see the examples


// First Option - Providing the type of each element. var is also allowed.
(string authorname, int age, var blog) = GetAuthor();
Console.WriteLine($"Author Details: Name: {authorname}, Age: {age}, BlogURL : {blog ?? "URL not available" } ");

// Second Option - Using var outside of the parenthesis
var (authorname, age, blog) = GetAuthor();
Console.WriteLine($"Author Details: Name: {authorname}, Age: {age}, BlogURL : {blog ?? "URL not available" } ");

// Third option - Using existing variables
string authorname = "Brij";
int age = 32;
string blog = "https://codewala.net/";

(authorname, age, blog) = GetAuthor();
Console.WriteLine($"Author Details: Name: {authorname}, Age: {age}, BlogURL : {blog ?? "URL not available" } ");			

Now it may happen that you are not sure about all the elements or want to discard few , you can use underscore (_) as

var (authorname, age, _) = GetAuthor();
Console.WriteLine($"Author Details: Name: {authorname}, Age: {age}");

Last thing, as we have now System.Tuple and System.ValueTuple both, ValueTuple provide a nice extension method as ToTuple() to convert it to System.Tuple.

C# 7.1 Enhancements: 

There are a small enhancement in C# 7.1 which can save few keystrokes as now elements names are inferred from the variables. Let’s see the example

// Earlier
string name = "Brij";
int age = 32;
string blog = "https://codewala.net/";
var author = (name: name, age: age, blog: blog);

// With C# 7.1 
string name = "Brij";
int age = 32;
string blog = "https://codewala.net/";
var author = (name, age, blog); // Element names would be - name, age, blog

Hope you have enjoyed this post and will be able to use in your day to day coding.

Cheers,
Brij

Use the awesomeness of Pattern Matching with C# 7.0

Pattern Matching is a new feature which was introduced with C# 7.0 which allows us to write cleaner and concise code in many different scenarios. This feature can be said as an extension of is and as operators that we already have in C#. I wrote a post on it earlier, you can take a look here. This feature can be broadly devivded in two sections

  1. Using Is Expression
  2. Using Pattern Matching in Switch Statements

Using Is Expression:

Prior to C# 7.0, Is operator was used to check the type of a variable and based on the type, it returns true or false but with C# 7.0, Is Expression provides following three types of pattern matching

  1. Const Pattern
  2. Type Pattern
  3. Var Pattern

Let’s discuss each with examples

Const Pattern: It allows us to check an object with any value. Let’s see an example

static void IsConstExpression()
{
    Object obj = 2;
    string name = "Brij";

    // null check
    if (obj is null)
        Console.WriteLine("Obj is null");

    // Constant value check
    if(obj is 2)
        Console.WriteLine("Obj has value 2");

    // String value check
    if(name is "Brij")
        Console.WriteLine("name has value \"Brij\"");
}

Above, we can see that we can check to any value including null.

Type Pattern: It allows us to confirm the type of the object and also assigns the value to a new variable of the given type. Prior to C# 7.0, we also had the similar feature but here we can assign to the new variable as mentioned. Lets see the example

static void IsTypeExpression()
{
    Object obj = 2;

    var objPerson = new Person() { FirstName = "Brij", LastName="Mishra" };
    var objNewPerson = new Employee() { FirstName = "Anvit", LastName = "Mishra", Company ="ABC Ltd" };

    if (obj is int i)
        Console.WriteLine($" Variable i has the value {i}");

    if (objPerson is Person person)
        Console.WriteLine($" p is of type {person.GetType().Name} and first name is {person.FirstName}");

    if (objNewPerson is Employee newPerson)
        Console.WriteLine($" p is of type {newPerson.GetType().Name} and first name is {newPerson.Company}");

    if (objNewPerson is Person objPer)
        Console.WriteLine($" p is of type {objPer.GetType().Name} and first name is {objPer.FirstName}");

}

Lets see the output

 

Here Employee inherits from Person. So in the last statement, we have the actual object of Employee but it assigned to a variable of base type.

Var Pattern: This is special case pattern where we check the type as var. This has one difference with the type pattern as it returns true even if it is null. Let’s see example

static void IsVarExpression()
{
    Object obj = new Person() { FirstName = "Brij", LastName = "Mishra" };

    if (obj is var p)
    {
        Console.WriteLine($"Var Pattern : P is of type {p?.GetType().Name}.");
    }

    obj = null;

    if (obj is var per)
    {
        Console.WriteLine($"Var Pattern : P is of type {per?.GetType().Name}.");
    }
}

The output will be as

Here we can see that the second check is also true but since it is null, nothing it displayed where we wrote the type name. Now lets move to switch statements.

Pattern Matching in Switch Statements:

The patterns that we discussed in previous section, can be leveraged in switch statements as well. This becomes very handy when the number of testing conditions grows and using Is pattern becomes tough to maintain.

Earlier switch statement was only supporting constant pattern with limited value types and strings but now we can use Type and var patterns as well. Let’s see the example

switch(p)
{
    case Manager objM:
        Console.WriteLine("p is of Manager type");
        break;
    case Employee objE:
        Console.WriteLine("p is of Employee type");
        break;
    case Person objP:
        Console.WriteLine("p is of Person type");
        break;
    case null:
        Console.WriteLine("p is null");
        break;
}

Here Person is the base class and with the hierarchy Person->Employee->Manager. Based on the type of p case statement gets executed and in case of null, last one gets executed. Here, the key is the most derived type should be first statement. Compiler also gives a warning if the order is not correct. C# 6.0 also provides us capability to use When clause in switch case. Let’s see the example

switch(p)
{
    case Employee objE when objE.Grade == 5:
        Console.WriteLine($"{objE.FirstName} is Manager");
        break;
    case Employee objE when objE.Grade == 5 && objE.Rating >= 3:
        Console.WriteLine($"{objE.FirstName} is Manager and eligible for additional bonus");
        break;
    case var objVar:
        Console.WriteLine("P is not a Employee and is of Type {objVar?.GetType().Name}   ");
        break;
}

Here we can see we can add additional filters in case statements which can be very useful in many scenarios. It also allows to add more that one filter and have various kind of combinations. I have used the var pattern as well in last case statement.

Hope you have enjoyed the post and will be able to use this feature in your day to day work.

Cheers,
Brij

How to use Null Conditional operators

Null values are very special in any language, specifically in C#. Every .NET developer must have pulled his/her hair at some point or other while dealing with it. C# is getting mature by adding more capabilities to handle the null values so that we don’t need to write long repetitive code to handle it. This operator was introduced with C# 6.0 sometimes also referred as safe navigation operator, and can be panacea for the most common NullReferenceException. There are few related topics like Null Coalescing operator, Nullable types, which I will advise to take a quick look before proceeding.

What is Null Conditional Operator?

This is a new operator introduced with C# 6.0, helps in performing null check while accessing its members. It provides following two syntax

  1. First operator: ?.   (Also called elvis operator)
  2. Second operator: ?[

Let’s see it with examples

First Null Conditional Operator (?.):

This operator allows us to access the members or elements of the provided instance only when it is not null. So before moving further, lets create few classes for the example

public class Person
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    public int Age { get; set; }

    public List <Address> Addresses { get; set;}

    public Person Spouse {get; set;}
}

public class Address
{
    public string Address1 { get; set; }
    public string Address2 { get; set; }

    public string City { get; set; }

    public string State { get; set; }

    public string Zip { get; set; }
}

If you have to access properties of the person, the usual way of doing it

if(p != null)
{
    string name = p.FirstName;
    int age = p.Age;
}

Now lets see using the ?. operator

string name = p?.FirstName;
int? age = p?.Age;

Here we dont need to have a null check as it is taken care by the null conditional operator. name is assigned to null if either object p is null or FirstName is null. While for age, I had to change the age variable as Nullable type because for value types, this operator returns a nullable type which is easily understandable as it would have no value (or null) if p is null.

Now if want to access the properties of Spouse then normally code would be as

if(p != null && p.Spouse != null)
{
    string name = p.Spouse.FirstName;
    int age = p.Spouse.Age;
}

which can be written as

string name = p?.Spouse?.FirstName;
int? Age = p?.Spouse?.Age;

Here, we avoided two null check and code looks much cleaner and concise. This operators becomes more helpful for the descending types. You must have written similar code like below numerous times while handling a service response

if (response != null && response.Results != null && response.Results.Status == Status.Success)
{
    // Handle response
}

this can be as

if (response?.Results?.Status == Status.Success)
{
        // Handle response
}

It looks super clean now. It could be more granular based on the scenario. Now let’s see another operator.

Second Null Conditional Operator (?[): This operator allows you to have a check over index operator. Let’s see the example.
Here I want to see the city of the second address of the person so normally, we will write it as

if(p!=null && p.Addresses != null && p.Addresses.Count > 1)
{
    string city = p.Addresses[1].City;
}

This we can write now as

string city = p?.Addresses?[1]?.City;

Now you can assume if I have read the same for spouse then how consize code would be.

Other Usages:
It can be used while calling method of instance like

p?.ToString();

We can use it with delegate and events as well like

myCustomDelegate?.Invoke(args)

// Note : myCustomDelegate?(args) won't work and it will be an compile time error

myCustomEvent?.Invoke(this, args);

I found this feature very useful in our day to day coding as we save lot of repetitive code. Hope you find it useful as well.

Cheers,
Brij

String Interpolation in C# with Examples

String is one of the most used types in C# and it provides many options playing with it. I wrote a post earlier where I discussed about String, StringBuilder and String.Fromat. You might want to have a look here. Today I am going to one of the very nice features that got introduced with C# 6, named String Interpolation.

What is String Interpolation?

String Interpolation is a process of generating the output string from a string literal by replacing the placeholders with the actual values. These placeholders could be just variable names or some expressions. It is like template processing where the variables are replaced with actual values to generate the final output. We already have String.Fromat where the values are replaced based on the indexing of provided parameters but we don’t need that now. Interpolation is very common feature in many new libraries and frameworks like Angular.

We will see multiple examples based on various usage of string interpolation. Lets start with basic one

Example 1:

string name = "Brij";
string topic = "String Interpolation";

// Prior to C# 6
Console.WriteLine(string.Format("Hello {0}. Lets learn {1}",name, topic));

// C# 6 and later
Console.WriteLine($"Hello {name}. Lets learn {topic}");

Here both will give the same output. The second option is much cleaner and readable.  As in the above example, to use it, the string should start with $. Let’s see the syntax of interpolated string

$"<text> {<expression> [,<field-width>] [:<format-string>] } <text> ..."  
  • field-width – It defines the width of the field. If positive then value is right aligned and if negative, it is left aligned. If the value is less than the width of the value, there is no impact in the output.
  • format-string – It can be used to define the format of the value like datetime, currency, number etc.

Note – There should be no space between $ and ” at the start of the string else it will htow an compile time error.
Example 2:

int langversion = 6;
string VSVersion = "Visual Studio 2015";
DateTime releaseDate = new DateTime(2015, 7, 20);

Console.WriteLine($"C# {langversion: 0.0} was released with {VSVersion} on {releaseDate: MMM d yyyy}.");

// output

C#  6.0 got released with Visual Studio 2015 on  Jul 20 2015.

If we have any special characters that could provide different meaning to literal then it should be escaped like “, \ etc . If we want a curly braces ({ or }) in the string then it should be written twice as {{ or }}. To use few language elements like colon (:) in expression, it should be delimited by parenthesis as well in expression.

Example 3:

Console.WriteLine($"We can use special meaning characters like \", \\ by escaping it in literal text.");
Console.WriteLine($"We can use {{curly braces}} by using it twice.");
Console.WriteLine($"To use it in expression it should be delimited by paranthesis"
+$" like  2*2 = 4 is {(2*2 == 4? "Correct" : "Incorrect")}");

// Output
We can use special meaning characters like ", \ by escaping it in literal text.
We can use {curly braces} by using it twice.
To use it in expression it should be delimited by paranthesis like  2*2 = 4 is Correct

In the above example, we have seen that how to use special characters in string literals and in expression. Let’s see one more example

Example 4:

Console.WriteLine($"3 power 4 using Math function { Math.Pow(3, 4)} and using custom power "
$"function { CustomPow(3, 4)}.");

// Output
3 power 4 using Math function 81 and using custom power function 81.

Here we can see that we can use any framework class or even custom function in this expression.

Hope you have enjoyed this feature and will start using it.

Cheers,
Brij

What are Immutable types?

In C#, primarly we have two types of objects: reference type and value type. Value type objects always have default value and created on stack. When we assign value type variable to another variable, a new copy gets created. While reference type objects default to null and created on heap. Multiple variables can point to the same object, it means changing the value using one, will reflect accross variables. There is one more type called Nullable type which is similar to value type with additional capability to have no value if it is unassigned. You can learn more about from one of my previous posts here

A reference type can be categorized in two types : Mutable and Immutable. The plain english meaning is “Can Change” and “Cannot Change” respectively and which is same here as well.

It means an Immutable type object cannot be changed after it’s creation/initialization and if one tries to change, a new copy gets created (if allowed) and returned. In other words, it is a reference type but having value type semantics. String is one of the most used immutable types and it is provided by the .NET framework.

Normal class that we create, are mutable type. Let’s see an example

    class Program
    {
        static void Main(string[] args)
        {
            Person objPerson = new Person() { Name = "Brij", Age =32 };
            UpdatePerson(objPerson);
            Console.WriteLine(objPerson.Name);
            Console.ReadKey();
        }

        static void UpdatePerson(Person P)
        {
            P.Name += " Mishra";
        }
    }

    public class Person
    {
        public string Name { get; set; }

        public int Age { get; set; }
    }

So in this example the output will be Brij Mishra as the same object got changed. This class can also be modified as where we just provide the getter and the values then can be modified either at constructor or any other method inside the same class.

public class Person
{
    private string _name;
    public string Name { get { return _name; } }

    private int _age;
    public int Age { get { return _age; } }

    public Person(string name, int age)
    {
        this._name = name;
        this._age = age;
    }
}

Now to make it an immutable object, we have two options:

  1. Use Const
  2. Use Readonly

So I can make the class as

   public class Person
    {
        private readonly string _name;
        public string Name { get { return _name; } }

        private readonly int _age;
        public int Age { get { return _age; }  }

        public Person(string name, int age)
        {
            this._name = name;
            this._age = age;
        }
    }

Now once we create an instance of this class, it cannot be updated as all the properties are readonly. Even, we cannot update in another new method in the same class as in the previous example. We can use the Const instead of readonly but in that case, we will loose the ability to assign the value while object creation, instead we will have to provide the value at class definition. One more drawback, as const variable initialized at Class level itself, also called compile time constant so it would be same for all the instances of that type.

Now lets create another class address and have a List of Addresses in the class as

 public class Person
    {
        private List
<Address> _addresses;
        private readonly string _name;
        public string Name { get { return _name; } }

        private readonly int _age;
        public int Age { get { return _age; }  }

        public Person(string name, int age, List
<Address> addresses)
        {
            this._name = name;
            this._age = age;
            _addresses = addresses;
        }
        public List
<Address> Addresses { get { return _addresses; } }
    }

    public class Address
    {
        public string Address1 { get; set; }

        public string Address2 { get; set; }

        public string City { get; set; }

        public string State { get; set; }

        public string Zip { get; set; }
    }

As here the list of address has only get property exposed, it means we cannot replace the whole collection but certainly we can update the items from the list by adding and/or removing an item as

Person objPerson = new Person("Brij", 32, addresses);
objPerson.Addresses.Add(new Address());

Now, to make the Person class Immuatble, we need to change it as readonly collection as

public class Person
{
    private List
<Address> _addresses;
    private readonly string _name;
    public string Name { get { return _name; } }

    private readonly int _age;
    public int Age { get { return _age; }  }

    public Person(string name, int age, List
<Address> addresses)
    {
        this._name = name;
        this._age = age;
        _addresses = addresses;
    }

    public ReadOnlyCollection
<Address> Addresses { get { return _addresses.AsReadOnly(); } }
}

Now we wont be able to add or remove items from list. Still we have here one gap and using we can update any existing address object as Address is not a immutable type.

To make it immutable we will require to make all the properties readonly or const.

So to make an object immuatble, all the internal type used, should also be immutable and all the collection should be readonly.

C# 6 added a feature that says if we have a auto property with only a getter then it can be only initialized in constructor. Behaind the scene, it uses private readonly property as

public class Person
{
    public string Name { get; }

    public int Age { get; }
}

Here if we try to update the properties other than the constructor, it will throw an error stating that it is readonly.

Hope you all have enjoyed the post.

Cheers
Brij