Cross-library Privacy

About

Library Boundaries: Privacy enforcement
Exports: Controlling what’s exposed
Hiding Implementation: src/ convention
Package Design: Public vs private APIs

Main Topics

Library Exports

Definition: Selective visibility

Example:

// lib/mylib.dart
export 'src/implementation.dart' show PublicClass;

Private Across Libraries
- Definition: True encapsulation
- Example:
```
// In library A:
class _Private {} // Inaccessible to B
```

Package Structure

Definition: Standard layout

Example:

my_package/
  lib/
    my_package.dart
    src/
      implementation.dart

Dependency Privacy
- Definition: Between packages
- Example:
```
// Can't access _ members
// from other packages
```

Visibility Testing

Definition: Verifying privacy

Example:

import 'package:other/other.dart';

void main() {
  // var x = _Private(); // Compile error
}

How to Use

API Design: Plan exports carefully
Implementation: Keep in src/
Documentation: Clearly mark public API
Versioning: Treat private as unstable

How It Works

Import Resolution: Analyzer checks access
Compilation: Enforces library boundaries
Package Layout: Convention over configuration
Pub: Respects privacy in dependencies

Example:

// Package structure:
// my_pkg/
//   lib/
//     my_pkg.dart        (exports)
//     src/
//       cache.dart       (private)
//       client.dart      (private)

// my_pkg.dart:
export 'src/client.dart' show PublicClient;

Conclusion

Cross-library privacy in Dart provides strong encapsulation between packages through rigorous enforcement of library boundaries. By properly organizing code into public exports and private implementations, package authors can maintain clean APIs while freely evolving their internal implementation details.