Is vs As operator in C#: Understanding the differences between is and as operator in C#

Last updated on March 1st, 2023 at 11:01 am

is vs as operator in c#:

In C#, the IS and AS operators are essential keywords used to determine the type of an object during runtime.
The IS operator checks the type of an object and returns a boolean value, which is true if the object is of the same type and false if not. On the other hand, the AS operator not only checks the type of an object but also performs a type conversion if the object is compatible with the given type.

TypeCasting is a common practice in software development often used to convert one object type to another.
However, this can sometimes result in exceptions such as “Cannot implicitly convert type ‘Object one’ to ‘object two’ or InvalidCastException”.

C# provides the IS and AS operators to address this issue. It offers a more efficient and refined casting and object compatibility checking approach.
By the end of this post, you will better understand the is and as operators and the knowledge to utilize them effectively in your applications.

C# IS Keyword:

The IS operator is a unary operator that determines whether an object is of a certain type. It returns a Boolean value (true or false) indicating whether the object is of the specified type or not.

Syntax

The syntax for the is operator is as follows:

object is Type

Example:

For example, Let’s consider the following code snippet to understand the is operator:

object obj = "hello";
bool isString = obj is string; // true

The is operator is used in the above example to determine whether the object obj is of the type string. The expression “obj is string” returns true, indicating that the object is of type string.

Here is another Example of IS operator.

using System;
namespace IsKeywordInCSharp
{
    class Animal { }
    class Dog : Animal { }
    class Cat : Animal { }

    class Program
    {
        static void Main(string[] args)
        {
            var animal = new Animal();
            var dog = new Dog();
            var cat = new Cat();

            bool isAnimal = animal is Animal; // returns true
            bool isDog = dog is Animal; // returns true
            bool isCat = cat is Animal; // returns true
            bool isCatDog = cat is Dog; // returns false    
            Console.WriteLine($" isAnimal: {isAnimal} ; isDog: {isDog} ; isCat: {isCat}; isCatDog: {isCatDog}");  
            Console.ReadLine();
        }
    }
}

The above example defines three classes: Animal, Dog, and Cat. We then create instances of each class and use the IS operator to check their types.
The first three lines of the code demonstrate that an object of each class can be identified as an instance of the Animal class.

The last line shows that an object of the type Cat cannot be identified as an instance of a Dog.

• Starting with C# 9.0, you can utilize a negation pattern for performing a non-null check using is operator, as demonstrated in the example below.

if (result is not null)
{
    Console.WriteLine(result.ToString());
}

• We can use the is operator to check for null, as the following example shows:

if (input is null)
{
    return;
}

• The is operator can be useful to check runtime type expressions:

using System;
public class IsOperatorExample
{
    public static void Main(string[] args)
    {
        int i = 35;
        object iBoxed = i;
        int? jNullable = 45;
        if (iBoxed is int a && jNullable is int b)
        {
            Console.WriteLine(a + b);  // output 80
        }
        Console.ReadLine();
    }
}

AS Operator in C#

The AS operator is a binary operator that performs a safe cast of an object to a specified type or returns null if the cast is not valid.

Syntax

The syntax for the as operator is as follows:

object as Type

Example

For example, Let’s consider the following code snippet to understand the as operator:

class Animal { }
class Dog : Animal { }

var animal = new Animal();
var dog = new Dog();

Animal animal1 = dog as Animal; // returns a valid cast
Dog dog1 = animal as Dog; // returns null

Output:

Valid cast
null

In the above example, we define two classes: Animal and Dog. We create instances of each class and use the AS operator to cast an object of type Dog to type Animal. Since Dog is a subclass of Animal, the cast is valid, and the Animal variable is assigned the dog object.

However, the second line shows that an object of type Animal cannot be cast as an instance of Dog, so the AS operator returns null.

Here is another example:

object obj = "hello";
string str = obj as string; // "hello"

In the above example, the as operator is used to determine if the object “obj” is of string type and also performs a type conversion. The result of the expression “obj as string” is “hello”, which is the value of the object after the type conversion.

It is important to note that if the object is not of the given type then the as operator will return null. For example:

object obj = 1;
string str = obj as string; // null

When to Use the is and as Operator in C#

The is operator is best used when you only need to check the type of an object and don’t need to perform any type conversions. The as operator is best used when you need to check an object’s type and perform a type conversion if the object is of the specified type.

Differences between IS and AS operator in C#

The following are a few differences between the is and as keywords in C#:

It’s important to note that the IS operator can be used in an if statement and As operator can be used in a try-catch statement.

Example: is vs as operator in C#

using System;
class Program
{
    static void Main(string[] args)
    {
        // Declare an object variable
        object obj = "hello";

        // Check if the object is of type string using the "is" operator
        if (obj is string)
        {
            Console.WriteLine("obj is of type string");
        }

        // Perform type conversion using the "as" operator
        string str = obj as string;

        // Check if the type conversion was successful
        if (str != null)
        {
            Console.WriteLine($"obj as string: {str}");
        }
        else
        {
            Console.WriteLine("obj is not of type string");
        }

        obj = 10;
        if (obj is string)
        {
            Console.WriteLine($"obj {obj} is of type string");
        }
        else
        {
            Console.WriteLine($"obj {obj} is not of type string");
        }
        str = obj as string;
        if (str != null)
        {
            Console.WriteLine($"obj as string: {str}");
        }
        else
        {
            Console.WriteLine($"obj {obj} is not of type string");
        }
        Console.ReadLine();
    }
}

The following output will be displayed once we run the above program:

Comparing IS and AS Operators in C#

Now that we know what the IS and AS operators are and how they work let’s compare their differences.

The primary difference between the IS and AS operators is that the IS operator returns a Boolean value, while the AS operator returns either a valid cast or null. In other words, the IS operator checks if an object is of a certain type, while the AS operator checks if an object can be cast as a certain type.

Here is an example that illustrates the difference:

class Animal { }
class Dog : Animal { }

var animal = new Animal();
var dog = new Dog();

if (dog is Animal)
{
    Animal animal1 = (Animal)dog;
    // do something with animal1
}

Dog dog1 = animal as Dog;
if (dog1 != null)
{
    // do something with dog1
}

Differences Between As and Is keywords in C#

Here are some other differences between the AS and IS operators in C#:

• We can only use the AS operator with reference types. We cannot use it with value types like int or float.
• We can use the IS operator with both reference and value types.
• The AS operator is more efficient than the IS operator since it only performs the cast once.
• The IS operator is more flexible than the AS operator since we can use it in a broader range of scenarios.

Advantages of AS over IS Operator

While both operators have their uses, there are some situations where the AS operator is preferred over the IS operator. Here are some advantages of AS over IS:

• The AS operator avoids the need for an explicit cast operator, making code more concise and readable.
• The AS operator provides a safe way to perform a cast and avoids potential runtime errors that can occur with an explicit cast operator.
• The AS operator allows for null values to be returned if the cast is not valid, avoiding the need for additional error handling code.

Conclusion

In conclusion, the IS and AS operators are essential tools in the C# developer’s toolbox. While they share some similarities, a few differences make them useful in different scenarios. The IS operator is useful for type checking, while the AS operator provides a safe way to perform a cast. Understanding these differences and use cases will allow you to write more efficient, concise, and error-free C# code.

FAQs

References-MSDN- is operator

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Shekh Ali

Meet Sheikh Ali, a skilled Software engineer and passionate a blogger. He enjoys sharing his expertise in C#, Java, SQL, Design Patterns, and other related topics through his writing. When he's not coding, Sheikh Ali can often indulge in his passions for reading books and fitness training.

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