Gain insights into Dart's object-oriented features, explore extensions, enums, mixins, and asynchronous programming. Discover hands-on code practice to confidently apply Dart in your projects.

dart.tar.gz

dart2_7

Dart is a fully object-oriented, class-based, simple, and clean language. Google’s popular mobile framework, Flutter uses Dart language to implement high-quality native applications, so it’s recommended that you understand Flutter before beginning this course.

In this course, you will dive deep into Dart 2 language features while using interactive hands-on code playgrounds. This course will help you become confident with Dart extensions, enums, mixins, generics, libraries, asynchronous programming, class variables, callable classes, and generator functions.

By the end of this course, you will have a strong understanding of Dart principles, and you’ll be ready to start using this powerful language in your own projects.

Developing Web Applications with Dart

# What Is a Conflict?

Imagine that you have a library/file to hold all common extensions of a project. Let's say this file is called 'extensions_lib.dart'.

The 'extensions_lib' has two extensions:
* An extension on `List` type named `MyList`. 
* An extension on `double` type named `MyDouble`.

## `MyList` Extension

The `MyList` extension defines a method `firstItem()` that returns the first element of the list. The return type is generic which is also represented as `T`. You will learn more about generics later in the course.

```dart
extension MyList<T> on List<T> {
    //Returns the first item in this list
    T first() => this[0];
}
```

## `MyDouble` extension

The `MyDouble` extension defines a method `tenTimes()` that returns ten times the double value it's called on.

```dart
extension MyDouble on double {
  double tenTimes() => this * 10;
}
```

## The 'extensions_lib.dart' File
Here are the contents of 'extensions_lib.dart':
```dart
extension MyList<T> on List<T> {
  //Returns the first item in this list
  T firstItem() => this[0];
}

extension MyDouble on double {
  double tenTimes() => this * 10;
}
```

## `main.dart`

The `main.dart` uses the extension methods to print the first item in a given list and also prints ten times the given double value.

The `MyList` extension's `firstItem()` method is used to print the first item on the list.

The `MyDouble` extension's `tenTimes()` method is used to print ten times the value of the given double.

To utilize the extensions defined in the file, you must import the 'extensions_lib.dart' file.

```dart
//importing extension methods
import 'extensions_lib.dart';

void main() {
  List<String> names = ["Priyanka", "Tyagi"];

  //print first name using extension
  print(names.firstItem());

  //Print MyDouble extension method `tenTimes()`
  print(10.0.tenTimes());
}
```

**Output:**
```notepad
Priyanka
100.0
```

So far, so good. Let's assume the `main.dart` file has another similar extension method `firstItem()` defined locally. See example below. 

```dart
extension<T> on List<T> {
  //Returns the first item in this list
  T firstItem() => this[0];
}
```
> A local extension is not required to be named.

Now, the following line in `main.dart` will throw a compile-time error since it is confused about which `firstItem()` to use.

```notepad
  print(names.firstItem());
```

## Try It Yourself
Run the code below to see the error caused by the conflicting extensions.

```notepad
main.dart:14:15: Error: The method 'firstItem' isn't defined for the class 'List<String>'.
 - 'List' is from 'dart:core'.
Try correcting the name to the name of an existing method, or defining a method named 'firstItem'.
  print(names.firstItem());
              ^^^^^^^^^
```

Learn to handle conflicts in similar named extensions.

Introduction

Dart Extensions

Dart Enums

Dart Mixins

Dart Generics

Dart Libraries

Asynchronous Programming In Dart

Miscellaneous

Next Steps

Extensions: Handling Conflicts

What Is a Conflict?