/ デザインパターン / Flyweight / Python Flyweight を Python で Flyweight は、 構造に関するデザインパターンの一つで、 メモリー消費量を低く抑えることで、 プログラムが膨大な数のオブジェクトを支えることができるようにします。 複数のオブジェクト間でオブジェクトの状態の一部を共有することにより、 これを実現します。 つまり、 Flyweight は、 異なるオブジェクトによって使われる同じデータをキャッシュすることにより、 RAM を節約します。 Flyweight の詳細 ナビゲーション はじめに 概念的な例 main Output 複雑度: 人気度: 使用例: Flyweight の目的はただ一つです: メモリー摂取を最小にする。 もしご自分のプログラムが RAM 不足で困っていない場合は、 このパターンのことはしばらく忘れて大丈夫です。 見つけ方: Flyweight は、 新規オブジェクトの代わりにキャッシュされたオブジェクトを返す生成メソッドの存在により識別できます。 概念的な例 この例は、 Flyweight デザインパターンの構造を説明するためのものです。 以下の質問に答えることを目的としています: どういうクラスからできているか? それぞれのクラスの役割は? パターンの要素同士はどう関係しているのか? main.py: 概念的な例 import json from typing import Dict class Flyweight(): """ The Flyweight stores a common portion of the state (also called intrinsic state) that belongs to multiple real business entities. The Flyweight accepts the rest of the state (extrinsic state, unique for each entity) via its method parameters. """ def __init__(self, shared_state: str) -> None: self._shared_state = shared_state def operation(self, unique_state: str) -> None: s = json.dumps(self._shared_state) u = json.dumps(unique_state) print(f"Flyweight: Displaying shared ({s}) and unique ({u}) state.", end="") class FlyweightFactory(): """ The Flyweight Factory creates and manages the Flyweight objects. It ensures that flyweights are shared correctly. When the client requests a flyweight, the factory either returns an existing instance or creates a new one, if it doesn't exist yet. """ _flyweights: Dict[str, Flyweight] = {} def __init__(self, initial_flyweights: Dict) -> None: for state in initial_flyweights: self._flyweights[self.get_key(state)] = Flyweight(state) def get_key(self, state: Dict) -> str: """ Returns a Flyweight's string hash for a given state. """ return "_".join(sorted(state)) def get_flyweight(self, shared_state: Dict) -> Flyweight: """ Returns an existing Flyweight with a given state or creates a new one. """ key = self.get_key(shared_state) if not self._flyweights.get(key): print("FlyweightFactory: Can't find a flyweight, creating new one.") self._flyweights[key] = Flyweight(shared_state) else: print("FlyweightFactory: Reusing existing flyweight.") return self._flyweights[key] def list_flyweights(self) -> None: count = len(self._flyweights) print(f"FlyweightFactory: I have {count} flyweights:") print("\n".join(map(str, self._flyweights.keys())), end="") def add_car_to_police_database( factory: FlyweightFactory, plates: str, owner: str, brand: str, model: str, color: str ) -> None: print("\n\nClient: Adding a car to database.") flyweight = factory.get_flyweight([brand, model, color]) # The client code either stores or calculates extrinsic state and passes it # to the flyweight's methods. flyweight.operation([plates, owner]) if __name__ == "__main__": """ The client code usually creates a bunch of pre-populated flyweights in the initialization stage of the application. """ factory = FlyweightFactory([ ["Chevrolet", "Camaro2018", "pink"], ["Mercedes Benz", "C300", "black"], ["Mercedes Benz", "C500", "red"], ["BMW", "M5", "red"], ["BMW", "X6", "white"], ]) factory.list_flyweights() add_car_to_police_database( factory, "CL234IR", "James Doe", "BMW", "M5", "red") add_car_to_police_database( factory, "CL234IR", "James Doe", "BMW", "X1", "red") print("\n") factory.list_flyweights() Output.txt: 実行結果 FlyweightFactory: I have 5 flyweights: Camaro2018_Chevrolet_pink C300_Mercedes Benz_black C500_Mercedes Benz_red BMW_M5_red BMW_X6_white Client: Adding a car to database. FlyweightFactory: Reusing existing flyweight. Flyweight: Displaying shared (["BMW", "M5", "red"]) and unique (["CL234IR", "James Doe"]) state. Client: Adding a car to database. FlyweightFactory: Can't find a flyweight, creating new one. Flyweight: Displaying shared (["BMW", "X1", "red"]) and unique (["CL234IR", "James Doe"]) state. FlyweightFactory: I have 6 flyweights: Camaro2018_Chevrolet_pink C300_Mercedes Benz_black C500_Mercedes Benz_red BMW_M5_red BMW_X6_white BMW_X1_red