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.