Add notes about Js, diffsitter and solid
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20220908193040-solid.org
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328
20220908193040-solid.org
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:PROPERTIES:
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:ID: b827c6e7-fe86-4301-a72c-dfaee85e142f
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:mtime: 20220910133550
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:ctime: 20220908193040
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:END:
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#+title: SOLID
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* Introduction
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* Cinq principes de design de classes (P.O.O),
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* Principes décrits par Robert J. Martin (a.k.a Uncle Bob) en 2000,
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* Acronyme créé par Michael Feathers.
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* Principes
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** Responsabilité unique (Single responsability principle)
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/A class should have one and only one reason to change, meaning that a class should have only one job./
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Exemple de classe réalisant différentes tâches:
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* Calcul du total de la facture (méthode ~calculate_total~),
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* Impression de la facture (méthode ~print_invoice~),
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* Sauvegarde de la facture (méthode ~save_to_file~).
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#+BEGIN_SRC python :results output
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class Invoice:
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def __init__(self, book, quantity, discount_rate, tax_rate, total):
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self.book = book
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self.quantity = quantity
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self.discount_rate = discount_rate
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self.tax_rate = tax_rate
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self.total = self.calculate_total()
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def calculate_total(self):
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price = (self.book.price - self.book.price * self.discount_rate) * self.quantity
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price_with_taxe = price * (1 + self.tax_rate)
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return price_with_taxe
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def print_invoice(self):
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print(f'{self.quantity}x {self.name} {self.price} $')
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print(f'Discount Rate: {self.discount_rate}')
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print(f'Tax Rate: {self.tax_rate}')
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print(f'Total: {self.total}')
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def save_to_file(self):
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# Creates a file with given name and writes the invoice
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...
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#+END_SRC
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Les erreurs :
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* La logique d'impression d'une facture (méthode ~print_invoice~) devrait étre isolée : la seule raison pour laquelle
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la classe ~Invoice~ devrait étre mise à jour est le changement de logique de calul du total (méthode
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~calculate_total~).
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* La logique de sauvegarde d'une facture (méthode ~save_to_file~) devrait elle aussi étre isolée : la classe ~Invoice~
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ne devrait pas étre mise à jour suite au changement de méthode de sauvegarde (passage d'un fichier à une BDD par ex).
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Une implémetation respectant le principe de *responsabilité unique* :
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#+BEGIN_SRC python :results output
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class Invoice:
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def __init__(self, book, quantity, discount_rate, tax_rate, total):
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self.book = book
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self.quantity = quantity
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self.discount_rate = discount_rate
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self.tax_rate = tax_rate
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self.total = self.calculate_total()
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def calculate_total(self):
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price = (self.book.price - self.book.price * self.discount_rate) * self.quantity
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price_with_taxe = price * (1 + self.tax_rate)
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return price_with_taxe
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class InvoicePrinter:
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def __init__(self, invoice):
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self._invoice = invoice
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def print(self):
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print(f'{self._invoice.quantity}x {self._invoice.name} {self._invoice.price} $')
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print(f'Discount Rate: {self._invoice.discount_rate}')
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print(f'Tax Rate: {self._invoice.tax_rate}')
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print(f'Total: {self._invoice.total}')
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class InvoicePersistance:
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def __init__(self, invoice):
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self._invoice = invoice
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def save_to_file(self):
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# Creates a file with given name and writes the invoice
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...
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#+END_SRC
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** Ouvert-fermé (Open-close principle)
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/Objects or entities should be open for extension but closed for modification./
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Une classe doit étre *ouverte pour l'extension* et *fermée pour les modifications* :
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* Il doit étre possible d'ajouter une fonctionnalité à une classe sans modifier le code existant,
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* Réalisé à l'aide d'interfaces et classes virtuelles,
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Exemple de classe ne respesctant pas le principe :
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#+BEGIN_SRC python :results output
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class InvoicePersistance:
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def __init__(self, invoice):
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self._invoice = invoice
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def save_to_file(self):
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# Creates a file with given name and writes the invoice
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...
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def save_to_database(self):
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# Save the invoice to database
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...
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#+END_SRC
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Il ne devrait pas étre nécessaire de modifier la classe ~InvoicePersistance~ lorsqu'une nouvelle manière de sauvegarder
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une ~Invoice~ est requise.
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Une implémetation respectant le principe *ouvert/fermé* :
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#+BEGIN_SRC python :results output
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from abc import abstractmethod
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class InvoicePersistance():
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def __init__(self, invoice):
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self._invoice = invoice
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@abstractmethod
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def save(self):
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...
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class FileInvoicePersistance(InvoicePersistance):
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def save(self):
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# Creates a file with given name and writes the invoice
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...
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class DatabaseInvoicePersistance(InvoicePersistance):
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def save(self):
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# Save the invoice to database
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...
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#+END_SRC
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** Principe de substitution de Liskov
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/Let q(x) be a property provable about objects of x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T./
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Les classes filles doivent pouvoir être substituées par leur classe mère :
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* Pour une classe B, fille de A, il doit être possible de passer une instance de B à toute méthode s'attendant à avoir une instance de A, sans disfonctionnement.
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#+BEGIN_SRC python :results output
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class Rectangle:
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def __init__(self, width, height):
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self._width = width
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self._height = height
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@property
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def width(self):
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return self._width
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@width.setter
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def width(self, width):
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self._width = width
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@property
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def height(self):
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return self._height
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@height.setter
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def height(self, height):
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self._height = height
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def get_area(self):
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return self._width * self._height
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class Square(Rectangle):
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def __init__(self, size):
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super().__init__(size, size)
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@Rectangle.width.setter
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def width(self, size):
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self._width = size
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self._height = size
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@Rectangle.height.setter
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def height(self, size):
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self._width = size
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self._height = size
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def test_get_area(rectangle):
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width = rectangle.width
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rectangle.height = 10
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print(f'Expected area of {10 * width}, got {rectangle.get_area()}')
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rectangle = Rectangle(2, 3)
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test_get_area(rectangle)
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square = Square(2)
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square.width = 5
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test_get_area(square)
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#+END_SRC
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#+RESULTS:
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: Expected area of 20, got 20
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: Expected area of 50, got 100
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La classe ~Square~ ne respecte pas le principe car le comportement de la méthode ~get_area~ diffère selon l'instance de
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classe passée en paramètre.
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** Principe de ségrégation d'interface (Interface segregation principle)
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/A client should never be forced to implement an interface that it doesn’t use, or clients shouldn’t be forced to depend on methods they do not use./
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Il s'agit d'un principe de séparation des interfaces : plusieurs interfaces spécifiques sont meilleures qu'une unique
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générale. Ainsi, seules les méthodes nécessaires sont implémentées et non l'intégralité de celles définies par
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l'interface générique.
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Exemple d'implémentation ne respectant pas le principe : l'interface ~ParkingLot~ englobe le stationnement
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ainsi que le paiement. Quid de son implémentation pour le cas d'un parking gratuit ?
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L'ideal serait d'isoler la partie paiement dans une interface dédiée.
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#+BEGIN_SRC python :results output
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from abc import abstractmethod
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class Car:
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...
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class ParkingLot:
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@abstractmethod
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def park_car(self):
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# Decrease empty spot count by 1
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...
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@abstractmethod
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def unpark_car(self):
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# Increase empty spot count by 1
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...
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@abstractmethod
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def get_capacity(self):
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# Return car capacity
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...
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@abstractmethod
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def calculate_fee(self, car):
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# Return the price based on the number of hours
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...
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@abstractmethod
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def do_payment(self, car):
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# Do the payment process for the computed fee
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...
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class FreeParking(ParkingLot):
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def park_car(self):
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...
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def unpark_car(self):
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...
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def get_capacity(self):
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...
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def calculate_fee(self, car):
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# Unused method here... the parking is free.
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...
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def do_payment(self, car):
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# Unused method here... the parking is free.
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...
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#+END_SRC
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** Principe d'inversion de dépendence (Dependency inversion principle)
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/Entities must depend on abstractions, not on concretions. It states that the high-level module must not depend on the
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low-level module, but they should depend on abstractions./
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Les classes devraient être baséees sur des interfaces ou des classes abstraites plutôt que des classes concrètes,
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#+BEGIN_SRC python :results output
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class SqlConnection:
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def connect(self):
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...
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class PasswordReminder:
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def __init__(self, connection: SqlConnection) -> None:
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...
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#+END_SRC
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La classe ~PasswordReminder~ ne doit pas avoir de couplage fort avec la méthode employée pour obtenir le mot de
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passe. L'usage d'une interface permettrait d'abstraire la méthode de collecte.
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#+BEGIN_SRC python :results outputs
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from abc import abstractmethod
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class Connection:
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@abstractmethod
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def connect(self):
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...
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class SqlConnection(Connection):
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def connect(self):
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...
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class PasswordReminder:
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def __init__(self, connection: Connection) -> None:
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...
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#+END_SRC
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* Références
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* [[https://fi.ort.edu.uy/innovaportal/file/2032/1/design_principles.pdf][Uncle bob design principes]]
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* [[https://www.freecodecamp.org/news/solid-principles-explained-in-plain-english/][SOLID principes explained in plain english - freecodecamp.org]]
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