Understanding the Spread Operator in Dart

2 min readAug 15, 2023

Understanding the Spread Operator in Dart

What is the Spread Operator?

The spread operator in Dart is denoted by three dots: .... It allows you to 'spread' the elements of a collection (like a List or a Set) into another collection. This operator is commonly used to merge or clone collections, make copies with modifications, and simplify code readability. Let’s have a look.

List<int> numbers = [1, 2, 3];
List<int> newNumbers = [...numbers, 4, 5];

print(newNumbers); // Output: [1, 2, 3, 4, 5]

In this example, the spread operator takes the individual elements of the numbers list and adds them to the newNumbers list, along with the new elements 4 and 5.

Merging Lists

The spread operator can be used to merge two lists seamlessly.

List<int> list1 = [1, 2, 3];
List<int> list2 = [4, 5, 6];
List<int> mergedList = [...list1, ...list2];

print(mergedList); // Output: [1, 2, 3, 4, 5, 6]

Copying Lists

Using the spread operator to copy a list ensures that modifications to one list won’t affect the other.

List<int> originalList = [10, 20, 30];
List<int> copiedList = [...originalList];

print(copiedList); // Output: [10, 20, 30]

Combining Lists with Modifications

List<int> baseList = [1, 2, 3];
List<int> modifiedList = [...baseList, 4, 5];

print(modifiedList); // Output: [1, 2, 3, 4, 5]

This demonstrates how you can create a new list based on an existing one, incorporating additional elements.

Benefits of the Spread Operator

Readability

The spread operator helps improve code readability by simplifying operations that involve collections.

Immutability

When creating copies or modified versions of collections, the spread operator ensures that the original collection remains unchanged.

Efficiency

Using the spread operator is generally more efficient than manual iteration when copying or merging collections.

Imagine you have different bowls of fruits. You want to combine them to make a colourful fruit salad. The spread operator is like a magical hand that picks up each fruit from the bowls and places them into the salad bowl. You can easily add new fruits to the salad without altering the original bowls.

Conclusion

The spread operator in Dart is a powerful tool that every mobile app developer should have in their toolkit. Its ability to efficiently merge, clone, and modify collections simplifies coding tasks and enhances code readability.