87. Collection initializers

After delving into the world of generic collections, you might be wondering if there’s a more concise way to populate collections right at the time of their declaration. Well, C# offers just that with collection initializers. This feature saves you the need for multiple Add calls and makes your code cleaner and easier to understand.

Key point

Collection initializers provide a shorthand for populating collections like List<T> and Dictionary<TKey, TValue> at the time of their instantiation. They improve code readability and reduce the lines of code needed for setup.

Collection initializers work like object initializers, but instead of setting properties on a single object, they allow you to add multiple elements to a collection. You’ve actually already seen collection initializers in action in the chapter on arrays.

Fig. 87.1 Much like dumping a bunch of books in a crate in one go, collection initializers allow you to populate collections, like lists and dictionaries, with multiple elements in a single line of code.

What are collection initializers?

In C#, collection initializers are a syntactic sugar that allows you to initialize collections with predefined elements in a single, concise statement.

Syntax of collection initializers

The general syntax for collection initializers involves declaring a new collection and immediately filling it with elements inside curly braces {}.

For lists, the syntax is straightforward:

// Using a collection initializer to create a list of integers.
var numbers = new List<int> { 1, 2, 3, 4 };

The below script needs to be able to find the current output cell; this is an easy method to get it.

The code above is equivalent to the code below.

// Creating an empty list of integers.
var numbers = new List<int>();

// Adding elements to the list one by one.
numbers.Add(1);
numbers.Add(2);
numbers.Add(3);
numbers.Add(4);

For dictionaries, the syntax involves key-value pairs:

// Using a collection initializer to create a dictionary.
var personInfo = new Dictionary<string, string>
{
    { "Name", "Alice" },
    { "Email", "alice@email.com" }
};

The following code is equivalent to the code above.

// Creating an empty dictionary.
var personInfo = new Dictionary<string, string>();

// Adding key-value pairs to the dictionary one by one.
personInfo.Add("Name", "Alice");
personInfo.Add("Email", "alice@email.com");

Warning

You can use collection initializers only when creating a collection. To add more elements later, you must use the Add method or other appropriate methods.

Note

The term ‘collection initializers’ is somewhat misleading because it’s not limited to collections but can be used for any enumerable with an Add method. We’ll talk more about enumerables in a later chapter but at this point we should mention that all collections are enumerables.

You can also use collection initializers with your own collections or enumerables (that have an Add method).

Conclusion

Collection initializers are a handy feature that lets you initialize collections like lists and dictionaries in a simple and readable manner. They don’t replace methods like Add but offer a more concise way to populate a collection upon its creation. Collection initializers can improve readability and maintainability.

Important

Use collection initializers judiciously. While they are convenient for small collections, for large or dynamically populated collections, using methods like Add may be more appropriate.