Working with Immutable Collections

Sometimes, we need to make a collection immutable, meaning that its members cannot change, i.e. we cannot add or remove them. If we import the System.Collections.Immutable namespace, then any collection that implements IEnumerable is given six extension methods to convert it into an immutable list, dictionary, hashset, and so on.

Creating an immutable list in C#

Let’s see a simple example of converting the cities list into an immutable list:

Step 1: In the WorkingWithCollections project, in Program.cs, import the System.Collections.Immutable namespace.

Step 2: In Program.cs, add statements to convert the cities list into an immutable list, and then add a new city to it, as shown in the following code: