Summary - Native extension
- Dart course
- Expert
- Lesson 24/47
- 5 min
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.
Practice 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());.
Starter code
void main() {
// define a StringEx extension (on String; shout and wordCount)
// print shout and wordCount calls
}Sample solution
extension StringEx on String {
String shout() => toUpperCase() + '!';
int wordCount() => split(' ').length;
}
void main() {
print('hello world'.shout());
print('hello world'.wordCount());
}Expected output
HELLO WORLD! 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How are extension methods resolved?
- Statically at compile time Correct answer
- Never resolved
- Dynamically at runtime
- In a subclass
Explanation: extension methods are resolved statically at compile time.
2 Match the extension concepts
| Term | Meaning |
|---|---|
extension method |
This access |
extension operator |
Operator overloading |
generic extension |
Type parameter |
subclass |
Inheritance and polymorphism |
3 An extension name
extension ____ on String {
String shout() => toUpperCase() + '!';
}extension StringShout on String {
String shout() => toUpperCase() + '!';
}Explanation: StringShout is the extension's name.