C# Cast method

The Cast<T>() method in C# is a LINQ extension method used to cast each element in a collection from one type to another. It is particularly useful when working with collections of object type that need to be converted to a specific type for further processing.

Syntax

Following is the syntax for the Cast<T>() method −

public static IEnumerable<TResult> Cast<TResult>(this IEnumerable source)

Parameters

• source − The collection containing elements to be cast.
• TResult − The target type to cast elements to.

Return Value

Returns an IEnumerable<TResult> containing each element of the source sequence cast to the specified type.

Using Cast() with Object Collections

When you have a collection of object type containing elements of a specific type, Cast<T>() converts them back to their original type −

using System;
using System.Linq;
using System.Collections.Generic;

class Program {
   static void Main() {
      List<object> myList = new List<object> { "Mac", "Windows", "Linux", "Solaris" };
      
      // Cast objects back to strings
      IEnumerable<string> stringList = myList.Cast<string>();
      
      foreach (string item in stringList) {
         Console.WriteLine(item);
      }
   }
}

The output of the above code is −

Mac
Windows
Linux
Solaris

Using Cast() with String Operations

Once cast to the proper type, you can chain additional LINQ methods like Select() to perform operations −

using System;
using System.Linq;
using System.Collections.Generic;

class Program {
   static void Main() {
      List<object> list = new List<object> { "keyboard", "mouse", "joystick", "monitor" };
      
      // Cast to string and get first 2 letters from every string
      IEnumerable<string> res = list.Cast<string>().Select(str => str.Substring(0, 2));
      
      foreach (string str in res) {
         Console.WriteLine(str);
      }
   }
}

The output of the above code is −

ke
mo
jo
mo

Using Cast() with Numeric Types

The Cast<T>() method also works with numeric types and other data types −

using System;
using System.Linq;
using System.Collections;

class Program {
   static void Main() {
      ArrayList numbers = new ArrayList { 10, 20, 30, 40, 50 };
      
      // Cast objects to integers and calculate sum
      int sum = numbers.Cast<int>().Sum();
      
      Console.WriteLine("Sum: " + sum);
      
      // Cast and filter even numbers
      var evenNumbers = numbers.Cast<int>().Where(x => x % 2 == 0);
      
      Console.WriteLine("Even numbers:");
      foreach (int num in evenNumbers) {
         Console.WriteLine(num);
      }
   }
}

The output of the above code is −

Sum: 150
Even numbers:
10
20
30
40
50

Conclusion

The Cast<T>() method is essential for converting collections of object type to strongly-typed collections, enabling type-safe operations and LINQ method chaining. It throws an exception if any element cannot be cast to the specified type, so ensure all elements are compatible before casting.