Dart: Mixing class
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Mixins are a way of defining code that can be reused in multiple class hierarchies. They are intended to provide member implementations en masse.
To use a mixin, use the with keyword followed by one or more mixin names. The following example shows two classes that use mixins:
class Musician extends Performer with Musical {
// ···
}
class Maestro extends Person with Musical, Aggressive, Demented {
Maestro(String maestroName) {
name = maestroName;
canConduct = true;
}
}
To define a mixin, use the mixin declaration. In the rare case where you need to define both a mixin and a class, you can use the mixin class declaration.
Mixins and mixin classes cannot have an extends clause, and must not declare any generative constructors.
For example:
mixin Musical {
bool canPlayPiano = false;
bool canCompose = false;
bool canConduct = false;
void entertainMe() {
if (canPlayPiano) {
print('Playing piano');
} else if (canConduct) {
print('Waving hands');
} else {
print('Humming to self');
}
}
}
Sometimes you might want to restrict the types that can use a mixin. For example, the mixin might depend on being able to invoke a method that the mixin doesn’t define. As the following example shows, you can restrict a mixin’s use by using the on keyword to specify the required superclass:
class Musician {
// ...
}
mixin MusicalPerformer on Musician {
// ...
}
class SingerDancer extends Musician with MusicalPerformer {
// ...
}
In the preceding code, only classes that extend or implement the Musician class can use the mixin MusicalPerformer. Because SingerDancer extends Musician, SingleDancer can mix in MusicalPerformer.
