Extensions in Dart

Lazar Nikolov

The Problem

Its not much of a solution to a problem, but a nice convenience. Extensions in Dart allow you to develop custom functionalities on any library or data structure, including your own. So how do we go about them?

The Solution

There&aspo;s a specific keyword in Dart used to create extensions: extension. When creating an extension we also need to specify on which data type it should apply. Lets say we want to make a few useful DateTime extension methods. We should create a separate file and create our date extensions inside:

// date_extensions.dart extension DateExtensions on DateTime { // ... }

Lets create an extension method that checks whether one date is at the same day as another:

extension DateExtensions on DateTime { bool isSameDay(DateTime other) { return this.year == other.year && this.month == other.month && this.day == other.day; } }

Note: Ive put this so you can see how the comparison happens. The IDE will most likely warn you: Don't access members with this unless avoiding shadowing.

We can use our new extension method like so (dont forget to import your dart extension file):


The this in our extension method refers to the date1 variable.

Aside from methods, we can also create getters, setters and operators as well. Heres a getter method that returns a date in a specific format:

extension DateExtensions on DateTime { // ... get formattedDate { DateFormat format; if (year != DateTime.now().year) { format = DateFormat("E, d MMM yyyy"); // we can also use other extension methods inside } else if (isToday()) { return "Today"; // we can also use other extension methods inside } else if (isYesterday()) { return "Yesterday"; } else { format = DateFormat("E, d MMM"); } return format.format(this); } }
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