Summary - Native extension

Combine extension methods, operators and generics to write a string helper extension.

Summary: Native extension

In this group we covered Dart extensions: an extension adds external methods to an existing type; an extension method accesses via this; an extension operator overloads operators.

A generic extension takes a type parameter; the extension vs subclass decision depends on state and polymorphism. In this summary you will write a string helper extension that combines all of these concepts.

Exercise Summary: A StringEx extension

Define a StringEx extension on String with two methods: String shout() => toUpperCase() + '!'; and int wordCount() => split(' ').length;. In main add print('hello world'.shout()); and print('hello world'.wordCount());.

Show example solution

extension StringEx on String {
  String shout() => toUpperCase() + '!';
  int wordCount() => split(' ').length;
}

void main() {
  print('hello world'.shout());
  print('hello world'.wordCount());
}

Test yourself

How are extension methods resolved?
- Statically at compile time
- Never resolved
- Dynamically at runtime
- In a subclass
Show answer

Statically at compile time — extension methods are resolved statically at compile time.
Match the extension concepts

extension method

This access
extension operator

Operator overloading
generic extension

Type parameter
subclass

Inheritance and polymorphism

An extension name

extension ____ on String {
  String shout() => toUpperCase() + '!';
}

Show answer

extension StringShout on String {
  String shout() => toUpperCase() + '!';
}

Next lesson: build_runner

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