Read-Only Structs: C# 7.2

C# supports two basic types : Value Type and Reference Type. The main difference between them where they get created: Value Types gets created in stack while Reference type in Heap. Other key difference, for ValueType whenever a parameter is passed as an argument, a copy gets created and passed while for reference types, refernce of the same onstance gets passed. There is another type called – Nullable Type but actually it’s a wrapper over value type. I wrote a post on it, you can have a look here.

All the Value Types internally inherits System.ValueType. Struct is also a ValueType which inherits same.

It’s a good idea to make struct immutable, it means once it is initalized, it cannot be modified. System.DateTime is an immutable Value Type. It provides many static methods but it always returns a new instance.

To make a struct immutable, the simple way to make all the members readonly and initializ these values via parameterized constructor. It’s members should be exposed via getter fields.

Let’s see an example

public struct Person
{
    public string FirstName { get; }

    public string LastName { get; }

    public int Age { get; }

    public Person(string firstName, string lastName, int age)
    {
        this.FirstName = firstName;
        this.LastName = lastName;
        this.Age = age;
    }
}

Above struct is immutable as there is no way to modify the initialized variable.

Read-Only structs:

Prior to C# 7.2, to create an Immutable value type, we had to write the struct in a way so that it doesn’t allow an update as in above example. If few fields are left without marking readonly/const unknowingly then it wont work as expected. C# 7.2 allows us to add readonly modifier before struct which makes sure thatg all the members are read only. If any member doesn’t, it will throw an error. Above struct can be marked as read only as

public readonly struct Person
{
    public string FirstName { get; }

    public string LastName { get; }

    public int Age { get; }

    public Person(string firstName, string lastName, int age)
    {
        this.FirstName = firstName;
        this.LastName = lastName;
        this.Age = age;
    }

}

One important thing, the parameterized constructor should be used to create the instance always else in case of using parameterless constructor use, the member would be set to default value which cannot be ever changed and we probably won’t want this. We cannot make parameter less private for struct in C# and even if there is a way we can bypass that. We can have some validate method which should be fired before using that struct’s memebers. I wont discuss this in details here.

Read-only struct provides framework support to write readonly struct and help us to avoid any unintended modification. In my previous post, I discussed about In modifier, it also can be used while passing any immutable object. These changes like ref, out, in etc in .NET framework got developed to make low level programming simpler and faster. Few more changes, we will be discussing in coming posts.

Note: If you are not sure how to use X# 7.2 (7.x) in your project, you may have a look on one of my previos post here.

Hope you enjoyed the post.

Cheers
Brij

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Using In Parameter Modifier : C# 7.2

Changes are the only constant thing in the world and that got little faster with C# new releases as we have minor now releases (also referred as point releases) with significant enhancements. New features are getting added and existing features are getting enhanced. In one my earlier posts, I discussed about Ref and Out improvements that took places in C# 7.0. You can go through the link below.

Ref and Out improvements in C# 7.0

Let’s have a quick look on it

Here we can see that if we want to pass the argument by ref then reference of the instance (value type or reference type) is passed and any change the in the argument in the called method reflects in the calling method as well.

Note – If you are curious about the using the ref keyword with reference type object, you can have a look to one of my previous posts by clicking here.

Out parameters, are also like pass by reference except it enforces a rule that calling method pass the variable without initializing while called method must initialize.

Say you have a big struct or any other value type, that you have to pass as an argument. Everytime you will call the method, a new copy will be created and passed to the method. If this has to be done multiple times then it can be a major performance issue.

Also, out keyword  forces to the called method to initialize the variable but we dont have opposite option. And ref keyword allows to pass the paramter via reference and here caller and called method both can modify the variable.

C# 7.2 introduced another keyword In which provides the ability to pass the argument as readonly. It fails at compile time if there is any code which tries to modify in the called method. The variable must be initialized before passing as a parameter.

Lets see an example

There are few restrictions.

  1. In, Out and Ref keywords cannot be used in async methods.
  2. Cannot be used in iterator methods (which has yield statements)
  3. Marking the arguments of main method as In, makes it invalid as entry method.

To summarize, In keyword can be really useful when you are passing a big value type object to method which is called multiple times because instead of creating a new copy in each call, it will be passed by reference.

Cheers,
Brij

How to use C# 7.2 (7.x – minor releases) in your Project

C# 7.0 and other minor releases (7.x) are loaded with many awesome features and I’ve been all those nice features recently. You can have a look here. I have seen many people facing issues with using these features. So in this quick post, I will discuss how you can leverage C# 7.x features.

Using Visual Studio 2017

To use C# 7.x features, Microsoft recommends to upgrade the IDE to Visual Studio 2017. To use C# latest minor releases C# 7.X (currently C# 7.2), this is not enough, we need to follow the below steps

  1. Right click on the project => Select Properties
  2. Select Build tab from the left pane.
  3. Go down and select Advanced button
  4. Select the Language version as

Here we can see tha the default selection is C# latest major version (default) which means 7.0. We also have the option to select specific versions like 7.0/7.1 but for 7.2, we need to select C# latest minor version (latest).

Using Visual Studio 2015

As mentioned above that Microsoft recommends to use Visual Studio 2017 for C# 7.x features but as these features are implemented by compiler so as long as your build is pointing to correct version of CSC, you can build the new features. However, Visual Studio 2015 may not like it as it doesn’t understand the new features and you may not get intellisense or any other IDE support.

To use C# 7.X in Visual Studio 2015, install the following nuget package

Microsoft.Net.Compilers

Once, you install this package, you should be able to use the latest language feature in VS 2015. However you might red   squiggly in the editor as

Here we can see that even the VS2015 editor is complaining but it is getting built.

Using System.ValueTuple

ValueTuple is not available by default as part of C# 7.0, we need to install following nuget package

System.ValueTuple

Hope you like the post and able to use the C# latest features.

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