Dart Academy · Lesson

on Constraints and Mixin Order

Restrict and stack mixins correctly.

Mixins With Requirements

Sometimes a mixin only makes sense on certain classes. Dart lets you set that rule with an on constraint, so misuse is caught early. 🔒

Adding on SomeType restricts where a mixin can be applied. Only classes that extend or implement that type may use it.

mixin Walker on Animal {
  void walk() => print('Walking');
}