Interface Classes

Interface Classes

About

  • Interface classes define pure contracts.
  • Support multiple implementation.
  • Enforce API compliance.
  • Promote loose coupling.

Main Topics

  1. Explicit Interfaces

    • Definition: interface modifier.
    • Example: 
      interface class DataStore {
  Future<Data> fetch();
}

  2. Implementation

    • Definition: implements keyword.
    • Example: 
      class SqlStore implements DataStore {
  @override
  Future<Data> fetch() {...}
}

  3. Multiple Interfaces

    • Definition: Composing contracts.
    • Example: 
      class FileCache implements Reader, Writer {...}

  4. API Design

    • Definition: Stable public contracts.
    • Example: 
      interface class PaymentGateway {
  Future<Receipt> charge(Amount amount);
}

How to Use

  • Declare: Use interface modifier
  • Implement: Use implements keyword
  • Compose: Multiple interfaces per class
  • Document: Clear contract definitions

How It Works

  • Enforcement: Must implement all members
  • Decoupling: Consumers depend on interfaces
  • Testing: Easy mocking of interfaces

Example Session:

void main() {
  DataStore store = SqlStore(); // Interface reference
  await store.fetch();
}

Conclusion

Interface classes enable robust system design through explicit contracts, facilitating testing, modularity, and future-proof API evolution in Dart codebases.