Feature request, Implement Multiton design pattern

[mbnadjib]

GetIt version: 5.0.1

It would be awsome if we can use Multiton pattern with GetIt.

I am actually developing flutter app which involve services, stores and allot of rxdart input / output streams.

i would like to instanciate / reuse / unregister objects on the fly based on an arbitrary tag (for example: 'category-1-products', 'category-2-products').

At first i went for using registerSingleton with an instanceName but this is not possible since i want to register all my objects at application startup using a setup() function and the tags / instanceName are not yet known.

i realy wanted to do it with GetIt so i figured a way to do it registerFactoryParam and using param1 as the tag

working example

class Product {
  static int instanceNumber = 0;
  final String label;

  Product(this.label) {
    instanceNumber++;
    print('New Instance label: ($label) number: (${instanceNumber})');
  }
}

void main() {
  GetIt.I.registerFactoryParam<Product, String, void>((name, _) {
    if (GetIt.I.isRegistered<Product>(instanceName: name)) {
      return sl<Product>(instanceName: name);
    } else {
      Product instance = Product(name);
      GetIt.I.registerSingleton<Product>(instance, instanceName: name);
      return instance;
    }
  });

  GetIt.I<Product>(param1: 'tag-1'); /// New singleton
  GetIt.I<Product>(param1: 'tag-2'); /// New singleton
  GetIt.I<Product>(param1: 'tag-1'); /// Reuse first singleton
}

I moved on and tried to make clean code so i went to extend GetIt implementation but found out that it is not possible since the _GetItImplementation class is not public

i ended up wrapping the whole library and adding / overriding GetIt methods when required by my app

Working example:

import 'package:get_it/get_it.dart';

/// Type definition for multiton registration callback
typedef MultitonFactoryFunc<T> = T Function(String tag);
class Sl {
  void registerMultiton<T>(MultitonFactoryFunc<T> func,
      {DisposingFunc<T> dispose}) {
    GetIt.I.registerFactoryParam<T, String, void>((tag, _) {
      if (GetIt.I.isRegistered<T>(instanceName: 'multiton-$tag')) {
        return GetIt.I<T>(instanceName: 'multiton-$tag');
      } else {
        T instance = func(tag);
        GetIt.I.registerSingleton<T>(
          instance,
          instanceName: 'multiton-$tag',
          dispose: dispose,
        );
        return instance;
      }
    });
  }

  T get<T>({String instanceName, dynamic param1, dynamic param2, String tag}) {
    assert(tag == null || (param1 == null && param2 == null),
    'cannot use params and tags at the same time');
    return GetIt.I<T>(
        instanceName: instanceName,
        param1: tag != null ? tag : param1,
        param2: param2);
  }

  T call<T>({String instanceName, dynamic param1, dynamic param2, String tag}) {
    return get<T>(
        instanceName: instanceName, param1: param1, param2: param2, tag: tag);
  }

  void unregister<T>(
      {Object instance,
        String instanceName,
        String tag,
        void Function(T) disposingFunction}) {
    GetIt.I.unregister<T>(
      instance: instance,
      instanceName: tag != null ? 'multiton-$tag' : instanceName,
      disposingFunction: disposingFunction, /// this is not working, is submitted and issue see #138
    );
  }

  Future<void> allReady(
      {Duration timeout, bool ignorePendingAsyncCreation = false}) {
    return GetIt.I.allReady(
        timeout: timeout,
        ignorePendingAsyncCreation: ignorePendingAsyncCreation);
  }

  void registerSingleton<T>(T instance,
      {String instanceName, bool signalsReady, DisposingFunc<T> dispose}) {
    return GetIt.I.registerSingleton(instance,
        instanceName: instanceName,
        signalsReady: signalsReady,
        dispose: dispose);
  }
}

Sl sl = Sl();

class Products {
  static int instanceNumber = 0;
  final String categoryLabel;

  Products(this.categoryLabel) {
    instanceNumber++;
    print('New Instance label: ($categoryLabel) number: ($instanceNumber)');
  }

  @override
  String toString() {
    return 'Product: $categoryLabel';
  }

  void dispose() {
    print('never called issue #138');
  }
}

void main() {
  /// Register once use everywhere
  sl.registerMultiton<Products>((tag) => Products(tag), dispose: (p) {
    p.dispose();
  });

  /// instanciate / reuse 
  Products cat1 = sl<Products>(tag: 'category-1-products');
  Products cat2 = sl<Products>(tag: 'category-2-products');
  Products reuseCat1 = sl<Products>(tag: 'category-1-products');

  print(cat1);
  print(cat2);
  print(reuseCat1);

  /// unregister on the fly
  sl.unregister<Products>(tag: 'category-1-products');
}

[escamoteur]

Why to you need to register all your objects at startup? There is actually no need for that.
Could it be that in reality you want a factory that registers it created instances automatically inside GetIt? And that checks first if an instance with that name already exists?

[escamoteur]

closing this because of no reply