CherryPick #

cherrypick is a flexible and lightweight dependency injection library for Dart and Flutter. It provides an easy-to-use system for registering, scoping, and resolving dependencies using modular bindings and hierarchical scopes. The design enables cleaner architecture, testability, and modular code in your applications.

Table of Contents #

• Key Features
• Installation
• Getting Started
• Core Concepts
  • Binding
  • Module
  • Scope
  • Disposable
• Dependency Resolution API
• Using Annotations & Code Generation
• Advanced Features
  • Hierarchical Subscopes
  • Logging
  • Circular Dependency Detection
  • Performance Improvements
• Example Application
• FAQ
• Documentation Links
• Additional Modules
• Contributing
• License

Key Features #

• Main Scope and Named Subscopes
• Named Instance Binding and Resolution
• Asynchronous and Synchronous Providers
• Providers Supporting Runtime Parameters
• Singleton Lifecycle Management
• Modular and Hierarchical Composition
• Null-safe Resolution (tryResolve/tryResolveAsync)
• Circular Dependency Detection (Local and Global)
• Comprehensive logging of dependency injection state and actions
• Automatic resource cleanup for all registered Disposable dependencies

Installation #

Add to your pubspec.yaml:

dependencies:
  cherrypick: ^<latest_version>

Then run:

dart pub get

Getting Started #

Here is a minimal example that registers and resolves a dependency:

import 'package:cherrypick/cherrypick.dart';

class AppModule extends Module {
  @override
  void builder(Scope currentScope) {
    bind<ApiClient>().toInstance(ApiClientMock());
    bind<String>().toProvide(() => "Hello, CherryPick!");
  }
}

final rootScope = CherryPick.openRootScope();
rootScope.installModules([AppModule()]);

final greeting = rootScope.resolve<String>();
print(greeting); // prints: Hello, CherryPick!

await CherryPick.closeRootScope();

Core Concepts #

Binding #

A Binding acts as a configuration for how to create or provide a particular dependency. Bindings support:

• Direct instance assignment (toInstance(), toInstanceAsync())
• Lazy providers (sync/async functions)
• Provider functions supporting dynamic parameters
• Named instances for resolving by string key
• Optional singleton lifecycle

Example

void builder(Scope scope) {
  // Provide a direct instance
  bind<String>().toInstance("Hello world");

  // Provide an async direct instance
  bind<String>().toInstanceAsync(Future.value("Hello world"));

  // Provide a lazy sync instance using a factory
  bind<String>().toProvide(() => "Hello world");

  // Provide a lazy async instance using a factory
  bind<String>().toProvideAsync(() async => "Hello async world");

  // Provide an instance with dynamic parameters (sync)
  bind<String>().toProvideWithParams((params) => "Hello $params");

  // Provide an instance with dynamic parameters (async)
  bind<String>().toProvideAsyncWithParams((params) async => "Hello $params");

  // Named instance for retrieval by name
  bind<String>().toProvide(() => "Hello world").withName("my_string");

  // Mark as singleton (only one instance within the scope)
  bind<String>().toProvide(() => "Hello world").singleton();
}

⚠️ Important note about using toInstance in Module builder:

If you register a chain of dependencies via toInstance inside a Module's builder, do not call scope.resolve<T>() for types that are also being registered in the same builder — at the moment they are registered.

CherryPick initializes all bindings in the builder sequentially. Dependencies registered earlier are not yet available to resolve within the same builder execution. Trying to resolve just-registered types will result in an error (Can't resolve dependency ...).

How to do it right:
Manually construct the full dependency chain before calling toInstance:

void builder(Scope scope) {
  final a = A();
  final b = B(a);
  final c = C(b);
  bind<A>().toInstance(a);
  bind<B>().toInstance(b);
  bind<C>().toInstance(c);
}

Wrong:

void builder(Scope scope) {
  bind<A>().toInstance(A());
  // Error! At this point, A is not registered yet.
  bind<B>().toInstance(B(scope.resolve<A>()));
}

Wrong:

void builder(Scope scope) {
  bind<A>().toProvide(() => A());
  // Error! At this point, A is not registered yet.
  bind<B>().toInstance(B(scope.resolve<A>()));
}

Note: This limitation applies only to toInstance. With toProvide/toProvideAsync and similar providers, you can safely use scope.resolve<T>() inside the builder.

⚠️ Special note regarding .singleton() with toProvideWithParams() / toProvideAsyncWithParams():

If you declare a binding using .toProvideWithParams(...) (or its async variant) and then chain .singleton(), only the very first resolve<T>(params: ...) will use its parameters; every subsequent call (regardless of params) will return the same (cached) instance.

Example:

bind<Service>().toProvideWithParams((params) => Service(params)).singleton();
final a = scope.resolve<Service>(params: 1); // creates Service(1)
final b = scope.resolve<Service>(params: 2); // returns Service(1)
print(identical(a, b)); // true

Use this pattern only when you want a “master” singleton. If you expect a new instance per params, do not use .singleton() on parameterized providers.

ℹ️ Note about .singleton() and .toInstance():

Calling .singleton() after .toInstance() does not change the binding’s behavior: the object passed with toInstance() is already a single, constant instance that will be always returned for every resolve.

It is not necessary to use .singleton() with an existing object—this call has no effect.

.singleton() is only meaningful with providers (such as toProvide/toProvideAsync), to ensure only one instance is created by the factory.

Module #

A Module is a logical collection point for bindings, designed for grouping and initializing related dependencies. Implement the builder method to define how dependencies should be bound within the scope.

Example

class AppModule extends Module {
  @override
  void builder(Scope currentScope) {
    bind<ApiClient>().toInstance(ApiClientMock());
    bind<String>().toProvide(() => "Hello world!");
  }
}

Scope #

A Scope manages a tree of modules and dependency instances. Scopes can be nested into hierarchies (parent-child), supporting modular app composition and context-specific overrides.

You typically work with the root scope, but can also create named subscopes as needed.

Example

// Open the main/root scope
final rootScope = CherryPick.openRootScope();

// Install a custom module
rootScope.installModules([AppModule()]);

// Resolve a dependency synchronously
final str = rootScope.resolve<String>();

// Resolve a dependency asynchronously
final result = await rootScope.resolveAsync<String>();

// Recommended: Close the root scope and release all resources
await CherryPick.closeRootScope();

// Alternatively, you may manually call dispose on any scope you manage individually
// await rootScope.dispose();

Disposable #

CherryPick can automatically clean up any dependency that implements the Disposable interface. This makes resource management (for controllers, streams, sockets, files, etc.) easy and reliable—especially when scopes or the app are shut down.

If you bind an object implementing Disposable as a singleton or provide it via the DI container, CherryPick will call its dispose() method when the scope is closed or cleaned up.

Key Points

• Supports both synchronous and asynchronous cleanup (dispose may return void or Future).
• All Disposable instances from the current scope and subscopes will be disposed in the correct order.
• Prevents resource leaks and enforces robust cleanup.
• No manual wiring needed once your class implements Disposable.

Minimal Sync Example

class CacheManager implements Disposable {
  void dispose() {
    cache.clear();
    print('CacheManager disposed!');
  }
}

final scope = CherryPick.openRootScope();
scope.installModules([
  Module((bind) => bind<CacheManager>().toProvide(() => CacheManager()).singleton()),
]);

// ...later
await CherryPick.closeRootScope(); // prints: CacheManager disposed!

Async Example

class MyServiceWithSocket implements Disposable {
  @override
  Future<void> dispose() async {
    await socket.close();
    print('Socket closed!');
  }
}

scope.installModules([
  Module((bind) => bind<MyServiceWithSocket>().toProvide(() => MyServiceWithSocket()).singleton()),
]);

await CherryPick.closeRootScope(); // awaits async disposal

Tip: Always call await CherryPick.closeRootScope() or await scope.closeSubScope(key) in your shutdown/teardown logic to ensure all resources are released automatically.

Dependency Resolution API #

• resolve<T>() — Locates a dependency instance or throws if missing.
• resolveAsync<T>() — Async variant for dependencies requiring async binding.
• tryResolve<T>() — Returns null if not found (sync).
• tryResolveAsync<T>() — Returns null async if not found.

Supports:

• Synchronous and asynchronous dependencies
• Named dependencies
• Provider functions with and without runtime parameters

Using Annotations & Code Generation #

CherryPick provides best-in-class developer ergonomics and type safety through Dart annotations and code generation. This lets you dramatically reduce boilerplate: simply annotate your classes, fields, and modules, run the code generator, and enjoy auto-wired dependency injection!

How It Works #

1. Annotate your services, providers, and fields using cherrypick_annotations.
2. Generate code using cherrypick_generator with build_runner.
3. Use generated modules and mixins for fully automated DI (dependency injection).

Supported Annotations #

You can easily combine these annotations for advanced scenarios!

Field Injection Example #

import 'package:cherrypick_annotations/cherrypick_annotations.dart';

@injectable()
class ProfilePage with _\$ProfilePage {
  @inject()
  late final AuthService auth;

  @inject()
  @scope('profile')
  late final ProfileManager manager;

  @inject()
  @named('admin')
  late final UserService adminUserService;
}

• After running build_runner, the mixin _ProfilePage will be generated for field injection.
• Call myProfilePage.injectFields(); or use the mixin's auto-inject feature, and all dependencies will be set up for you.

Module and Provider Example #

@module()
abstract class AppModule {
  @singleton
  AuthService provideAuth(Api api) => AuthService(api);

  @named('logging')
  @provide
  Future<Logger> provideLogger(@params Map<String, dynamic> args) async => ...;
}

• Mark class as @module, write provider methods.
• Use @singleton, @named, @provide, @params to control lifecycle, key names, and parameters.
• The generator will produce a class like $AppModule with the proper DI bindings.

Usage Steps #

1. Add to your pubspec.yaml:

   dependencies:
     cherrypick: any
     cherrypick_annotations: any
   
   dev_dependencies:
     cherrypick_generator: any
     build_runner: any
   

2. Annotate your classes and modules as above.

3. Run code generation:

   dart run build_runner build --delete-conflicting-outputs
   # or in Flutter:
   flutter pub run build_runner build --delete-conflicting-outputs
   

4. Register modules and use auto-injection:

   final scope = CherryPick.openRootScope()
     ..installModules([$AppModule()]);
   
   final profile = ProfilePage();
   profile.injectFields(); // injects all @inject fields
   

Advanced: Parameters, Named Instances, and Scopes #

• Use @named for key-based multi-implementation injection.
• Use @scope when dependencies live in a non-root scope.
• Use @params for runtime arguments passed during resolution.

Troubleshooting & Tips #

• After modifying DI-related code, always re-run build_runner.
• Do not manually edit .g.dart files—let the generator manage them.
• Errors in annotation usage (e.g., using @singleton on wrong target) are shown at build time.

References #

• Full annotation reference (en)
• cherrypick_annotations/README.md
• cherrypick_generator/README.md
• See the examples/postly for a full working DI+annotations app.

Advanced Features #

Hierarchical Subscopes #

CherryPick supports a hierarchical structure of scopes, allowing you to create complex and modular dependency graphs for advanced application architectures. Each subscope inherits from its parent, enabling context-specific overrides while still allowing access to global or shared services.

Key Points

• Subscopes are child scopes that can be opened from any existing scope (including the root).
• Dependencies registered in a subscope override those from parent scopes when resolved.
• If a dependency is not found in the current subscope, the resolution process automatically searches parent scopes up the hierarchy.
• Subscopes can have their own modules, lifetime, and disposable objects.
• You can nest subscopes to any depth, modeling features, flows, or components independently.

Example

final rootScope = CherryPick.openRootScope();
rootScope.installModules([AppModule()]);

// Open a hierarchical subscope for a feature or page
final userFeatureScope = rootScope.openSubScope('userFeature');
userFeatureScope.installModules([UserFeatureModule()]);

// Dependencies defined in UserFeatureModule will take precedence
final userService = userFeatureScope.resolve<UserService>();

// If not found in the subscope, lookup continues in the parent (rootScope)
final sharedService = userFeatureScope.resolve<SharedService>();

// You can nest subscopes
final dialogScope = userFeatureScope.openSubScope('dialog');
dialogScope.installModules([DialogModule()]);
final dialogManager = dialogScope.resolve<DialogManager>();

Use Cases

• Isolate feature modules, flows, or screens with their own dependencies.
• Provide and override services for specific navigation stacks or platform-specific branches.
• Manage the lifetime and disposal of groups of dependencies independently (e.g., per-user, per-session, per-component).

Tip: Always close subscopes when they are no longer needed to release resources and trigger cleanup of Disposable dependencies.

Logging #

CherryPick lets you log all dependency injection (DI) events and errors using a flexible observer mechanism.

Custom Observers

You can pass any implementation of CherryPickObserver to your root scope or any sub-scope. This allows centralized and extensible logging, which you can direct to print, files, visualization frameworks, external loggers, or systems like Talker.

Example: Printing All Events

import 'package:cherrypick/cherrypick.dart';

void main() {
  // Use the built-in PrintCherryPickObserver for console logs
  final observer = PrintCherryPickObserver();
  final scope = CherryPick.openRootScope(observer: observer);
  // All DI actions and errors will now be printed!
}

Example: Advanced Logging with Talker

For richer logging, analytics, or UI overlays, use an advanced observer such as talker_cherrypick_logger:

import 'package:cherrypick/cherrypick.dart';
import 'package:talker/talker.dart';
import 'package:talker_cherrypick_logger/talker_cherrypick_logger.dart';

void main() {
  final talker = Talker();
  final observer = TalkerCherryPickObserver(talker);
  CherryPick.openRootScope(observer: observer);
  // All container events go to the Talker log system!
}

Default Behavior

• By default, logging is silent (SilentCherryPickObserver) for production, with no output unless you supply an observer.
• You can configure observers per scope for isolated, test-specific, or feature-specific logging.

Observer Capabilities

Events you can observe and log:

• Dependency registration
• Instance requests, creations, disposals
• Module installs/removals
• Scope opening/closing
• Cache hits/misses
• Cycle detection
• Diagnostics, warnings, errors

Just implement or extend CherryPickObserver and direct messages anywhere you want!

When to Use

• Enable verbose logging and debugging in development or test builds.
• Route logs to your main log system or analytics.
• Hook into DI lifecycle for profiling or monitoring.

Circular Dependency Detection #

CherryPick can detect circular dependencies in your DI configuration, helping you avoid infinite loops and hard-to-debug errors.

How to use:

1. Enable Cycle Detection for Development

Local detection (within one scope):

final scope = CherryPick.openSafeRootScope(); // Local detection enabled by default
// or, for an existing scope:
scope.enableCycleDetection();

Global detection (across all scopes):

CherryPick.enableGlobalCrossScopeCycleDetection();
final rootScope = CherryPick.openGlobalSafeRootScope();

2. Error Example

If you declare mutually dependent services:

class A { A(B b); }
class B { B(A a); }

scope.installModules([
  Module((bind) {
    bind<A>().to((s) => A(s.resolve<B>()));
    bind<B>().to((s) => B(s.resolve<A>()));
  }),
]);

scope.resolve<A>(); // Throws CircularDependencyException

3. Typical Usage Pattern

• Always enable detection in debug and test environments for maximum safety.
• Disable detection in production for performance (after code is tested).

import 'package:flutter/foundation.dart';

void main() {
  if (kDebugMode) {
    CherryPick.enableGlobalCycleDetection();
    CherryPick.enableGlobalCrossScopeCycleDetection();
  }
  runApp(MyApp());
}

4. Handling and Debugging Errors

On detection, CircularDependencyException is thrown with a readable dependency chain:

try {
  scope.resolve<MyService>();
} on CircularDependencyException catch (e) {
  print('Dependency chain: ${e.dependencyChain}');
}

More details: See cycle_detection.en.md

Performance Improvements #

Performance Note:
Starting from version 3.0.0, CherryPick uses a Map-based resolver index for dependency lookup. This means calls to resolve<T>() and related methods are now O(1) operations, regardless of the number of modules or bindings in your scope. Previously, the library had to iterate over all modules and bindings to locate the requested dependency, which could impact performance as your project grew.

This optimization is internal and does not change any library APIs or usage patterns, but it significantly improves resolution speed in larger applications.

Example Application #

Below is a complete example illustrating modules, subscopes, async providers, and dependency resolution.

import 'dart:async';
import 'package:meta/meta.dart';
import 'package:cherrypick/cherrypick.dart';

class AppModule extends Module {
  @override
  void builder(Scope currentScope) {
    bind<ApiClient>().withName("apiClientMock").toInstance(ApiClientMock());
    bind<ApiClient>().withName("apiClientImpl").toInstance(ApiClientImpl());
  }
}

class FeatureModule extends Module {
  final bool isMock;
  FeatureModule({required this.isMock});
  @override
  void builder(Scope currentScope) {
    // Async provider for DataRepository with named dependency selection
    bind<DataRepository>()
        .withName("networkRepo")
        .toProvideAsync(() async {
          final client = await Future.delayed(
            Duration(milliseconds: 100),
            () => currentScope.resolve<ApiClient>(
              named: isMock ? "apiClientMock" : "apiClientImpl",
            ),
          );
          return NetworkDataRepository(client);
        })
        .singleton();

    // Chained async provider for DataBloc
    bind<DataBloc>().toProvideAsync(
      () async {
        final repo = await currentScope.resolveAsync<DataRepository>(
            named: "networkRepo");
        return DataBloc(repo);
      },
    );
  }
}

void main() async {
  final scope = CherryPick.openRootScope().installModules([AppModule()]);
  final featureScope = scope.openSubScope("featureScope")
    ..installModules([FeatureModule(isMock: true)]);

  final dataBloc = await featureScope.resolveAsync<DataBloc>();
  dataBloc.data.listen(
    (d) => print('Received data: $d'),
    onError: (e) => print('Error: $e'),
    onDone: () => print('DONE'),
  );

  await dataBloc.fetchData();
}

class DataBloc {
  final DataRepository _dataRepository;
  Stream<String> get data => _dataController.stream;
  final StreamController<String> _dataController = StreamController.broadcast();

  DataBloc(this._dataRepository);

  Future<void> fetchData() async {
    try {
      _dataController.sink.add(await _dataRepository.getData());
    } catch (e) {
      _dataController.sink.addError(e);
    }
  }

  void dispose() {
    _dataController.close();
  }
}

abstract class DataRepository {
  Future<String> getData();
}

class NetworkDataRepository implements DataRepository {
  final ApiClient _apiClient;
  final _token = 'token';
  NetworkDataRepository(this._apiClient);

  @override
  Future<String> getData() async =>
      await _apiClient.sendRequest(
        url: 'www.google.com',
        token: _token,
        requestBody: {'type': 'data'},
      );
}

abstract class ApiClient {
  Future sendRequest({@required String? url, String? token, Map? requestBody});
}

class ApiClientMock implements ApiClient {
  @override
  Future sendRequest(
      {@required String? url, String? token, Map? requestBody}) async {
    return 'Local Data';
  }
}

class ApiClientImpl implements ApiClient {
  @override
  Future sendRequest(
      {@required String? url, String? token, Map? requestBody}) async {
    return 'Network data';
  }
}

FAQ #

Q: Do I need to use await with CherryPick.closeRootScope(), CherryPick.closeScope(), or scope.dispose() if I have no Disposable services? #

A:
Yes! Even if none of your services currently implement Disposable, always use await when closing scopes. If you later add resource cleanup (by implementing dispose()), CherryPick will handle it automatically without you needing to change your scope cleanup code. This ensures resource management is future-proof, robust, and covers all application scenarios.

Documentation Links #

• Circular Dependency Detection (En)(Ru)

Additional Modules #

CherryPick provides a set of official add-on modules for advanced use cases and specific platforms:

Contributors #

• Sergey Penkovsky
• Klim Yaroshevich
• Alexey Popkov

Contributing #

Contributions are welcome! Please open issues or submit pull requests on GitHub.

License #

Licensed under the Apache License 2.0.

Important: Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for specific language governing permissions and limitations under the License.

Links #

• GitHub Repository