Generics & Extension Methods

Use Generics & Extension Methods to express stable APIs and exhaustive domain models. Prefer composition, sealed hierarchies, constrained generics, and focused extensions while minimizing hidden mutation and unchecked casts.

Build a Complete Mental Model

Use Generics & Extension Methods to express stable APIs and exhaustive domain models. Prefer composition, sealed hierarchies, constrained generics, and focused extensions while minimizing hidden mutation and unchecked casts.

Apply It in Modern Dart

Run and test an original Generics & Extension Methods example with null, empty, boundary, invalid, async-error, and cancellation cases. Use dart format, dart analyze, and dart test, and verify Future or Stream subscriptions and isolate boundaries where relevant.

After This Lesson

• Explain nullability, mutability, and async contracts
• Write an example that passes dart analyze
• Test a failure or async case

T? firstOrNull<T>(List<T> values) => values.isEmpty ? null : values.first;

extension IntTotals on Iterable<int> {
  int get total => fold(0, (sum, value) => sum + value);
}

void main() {
  print(firstOrNull(<String>['Dart']));
  print([1, 2, 3].total);
}

Dart
6

Dart language overview — Dart