Xlab #2: wzorce projektowe

www.xsolve.plAgile Software House
Design patterns

Goals

1. 10:00 Przywitanie
2. 10:30 Dobre praktyki programowania
3. 11:00 Wzorce projektowe
○ Creational design patterns
○ Structural patterns
○ Behavioral design patterns
4. 12:00 Przerwa na pizzę
5. 12:30 Code Kata - Supermarket
6. 14:00 Analiza rozwiązań
7. 14:30 Podsumowanie
na żywych przykładach wspólnie przygotujemy SOLIDny kod
xlab #2: Wzorce projektowe agenda

Speakers

PHP Software Developer
Tomasz Łysek
Masterzu developerzu i architekturzu dla rozwiązań biznesowych od ok. 10 lat.
Woli backend i DB niż elementy frontu. Pilnuje by studenci pisali porządny kod.
W wolnym czasie gotuje, bije innych na treningach i relaksuje się przy zmywaniu naczyń.
"Wąż powiedział: choć ze mna pokażę Ci zalety JS-a. (...) Projekt osunął się powoli, jak
pada drzewo. Team Leader stłumił nawet odgłos upadku moralnego programisty."
Antoine de Saint-Exupéry

Senior PHP Software Developer
Mateusz Rosiek
Backend developer PHP od 5 lat. Aktualnie zajmuję się aplikacją wystawiającą API
RESTowe dla systemu e-commerce.
Prywatnie właściciel jeża.
“W nienawiści do JS tak zostałem wychowany
Hardcor PHP, ogień PHP”
~Paulo Coelho

Ion Bazan
PHP Developer, w XSolve od 9 miesięcy. Aktualnie zajmuje się projektem platformy
B2B/B2C dla branży oponiarskiej.
“They told me JS was fun but all I got was promises.”
~Paulo Coelho

Piotr Leśniowski
Jestę developerę. Programuję w PHP i JS w celu zarobkowym od 5 lat a hobbystycznie
od 8-ej klasy podstawówki. Romansowałem m. in. z C# i Pythonem, aczkolwiek
przygody te nie zakończyły się zdrowym i długotrwałym związkiem. Gdy nie
programuję, oddaję się słuchaniu muzyki, kolekcjonowaniu płyt, brawurowej jeździe
samochodem marki Cinquecento oraz denerwowaniu się na marne, kinowe adaptacje
gier. W młodości chciałem zostać śmieciarzem albo kierowcą rajdowym. Skończyło się
na wyłapywaniu śmieci w oprogramowaniu oraz na prawku kat. B. Aktualnie jestem
odpowiedzialny za projektowanie i utrzymywanie RESTowego API dla aplikacji SPA.
PS.
Lubię placki... i przemyślany kod.
PSS.
Czasami coś machnę w Angularze.

Your turn

Contract

● We would like to write SOLID code, so:
○ We need to know and use best practices
○ We need to know and use basic design patterns
○ We need to write tests
● We would like to have fun, eat pizza and drink beers! :)
What we want to achieve
Contract

SOLID

What is it?

“[SOLID] is a mnemonic acronym introduced by
Michael Feathers for the "first five principles" named
by Robert C. Martin in the early 2000s that stands for
five basic principles of object-oriented programming
and design”
- Wikipedia
What is it?

● Single responsibility principle
What is it?

● Open/Closed principle
What is it?

● Liskov substitution principle
What is it?

● Interface segregation principle
What is it?

What is it?
● Interface segregation principle
● Dependency inversion principle

Does my code stink?

Probably yes.

How do I know if my code stinks?

How do I know if my code stinks?
● Rigidity - design is hard or nearly impossible to change
● Fragility - design is easily breakable
● Solution is non-reusable
● Design makes it nearly impossible to do the right thing

Single responsibility principle
● If something is good for everything then it’s pretty much for nothing
● A class should only have one responsibility
● There shouldn’t be more than one reason for a class to change
● TL;DR - a class should focus on doing one thing and one thing only

Single responsibility principle

Open/closed principle
● A class should be open for extending
● A class should be closed for changes
● TL;DR - when requirements change we should extend the existing code,
not change it

Open/closed principle

Liskov substitution principle
● A class implementing an abstraction should do it properly. In a way that
the code that is based on the abstraction should not be dependant on
concrete implementations, but it should allow for substituting different
implementations of formentioned abstraction
● TL;DR - Subclasses should behave properly when substituted for base
class

Liskov substitution principle

Interface segregation principle
● Many client-specific interfaces are better than one general-purpose
interface
● A class should not be dependant on methods that it doesn’t use
● TL;DR - Avoid fat interfaces

Interface segregation principle

Dependency inversion principle
● A base class should not be dependant on subclass, both should be
dependant on abstraction
● TL;DR - Use interfaces and abstractions

Dependency inversion principle

Law of Demeter

Law of Demeter
● A principle of least knowledge
● A method of an object can call another method of:
○ The same object
○ Any parameter passed to it
○ Any object created by it
○ Direct component of an object to which it belongs
● TL;DR - Don’t talk to strangers

Design Patterns

Creational Design Patterns

Creational design patterns
● They are all about class instantiation
● They can be divided into class and object-creational patterns
● They encapsulate using new keyword to create objects

Can’t we just use
constructor?

No.

Abstract Factory
Provide a level of indirection that abstracts the creation of families of related or
dependent objects without directly specifying their concrete classes. The
"factory" object has the responsibility for providing creation services for the
entire platform family. Clients never create platform objects directly, they ask
the factory to do that for them.

Abstract Factory

Abstract Factory
● AbstractPizzaFactory provides a Factory Method for Pizza object.
● CapricciosaPizzaFactory and ProsciuttoPizzaFactory are concrete Pizza
factories extending/implementing AbstractPizzaFactory.
● Client does not have idea which concrete object the factory returns

Factory Method
Factory Method is to creating objects as Template Method is to implementing
an algorithm. A superclass specifies all standard and generic behavior (using
pure virtual "placeholders" for creation steps), and then delegates the creation
details to subclasses that are supplied by the client.

Factory Method

Factory Method
● Evaluates arguments and decides which derived object to create and
return
● Defines an interface for creating objects, but lets subclasses decide which
classes to instantiate

Builder
The Builder pattern separates the construction of a complex object from its
representation so that the same construction process can create different
representations. The focus/distinction is on creating complex aggregates.

Builder

Builder
● Separate the construction of a complex object from its representation so
that the same construction process can create different representations.
● Parse a complex representation, create one of several targets.

Test results

Structural Design Patterns

Private Data Class
● The private class data design pattern seeks to reduce exposure of attributes by
limiting their visibility. It reduces the number of class attributes by encapsulating
them in single Data object. It allows the class designer to remove write privilege of
attributes that are intended to be set only during construction, even from methods of
the target class.
Source: wikipedia
● Separates data from business logic.
● Encapsulates class data within two objects.
● Can be combined with Value Object pattern.
TL;DR: Get fields from your class and put them in separate (new) class.

Flyweight
● A flyweight is an object that minimizes memory use by sharing as much data as
possible with other similar objects.
Source: wikipedia
● Minimal structure.
● Simple interface.
● Easy to implement.
● Should implement Private Data Class or at least Value Object.
TL;DR: make multiple small classes from your big data business logic class
(get the core and put it into different class).

Facade
● A facade is an object that provides a simplified interface to a larger body of code,
such as a class library. The Facade design pattern is often used when a system is
very complex or difficult to understand because the system has a large number of
interdependent classes or its source code is unavailable. This pattern hides the
complexities of the larger system and provides a simpler interface to the client.
Source: wikipedia
● Simplify interface of complex class/classes.
● Provide new interface for class/classes.
TL;DR: If you have very complex class or subsystem just do one class facade
for simply to use interface.

Adapter
● Allows the interface of an existing class to be used as another interface. An adapter
helps two incompatible interfaces to work together. This is the real world definition
for an adapter. Interfaces may be incompatible but the inner functionality should suit
the need. The Adapter design pattern allows otherwise incompatible classes to work
together by converting the interface of one class into an interface expected by the
clients.
Source: wikipedia
● Create brand new interface for an existing class.
● Adapt system interface to clients needs.
● Best way to create new system with old system interface.
TL;DR: When there is a strong need to adapt created interface to new
requirements - make new class with needed methods and run in them the old
one’s

Adapter
Facade vs Adapter:
● Make new interface for existing one,
● Adapter uses already created interface,
● Facade create new interface from the scratch.
Adapter vs Bridge:
● If you use aggregation then make it in abstract and create bridge but if you use
inheritance then make adapter.

Proxy
● A proxy, in its most general form, is a class functioning as an interface to something
else. The proxy could interface to anything: a network connection, a large object in
memory, a file, or some other resource that is expensive or impossible to duplicate.
In short, a proxy is a wrapper or agent object that is being called by the client to
access the real serving object behind the scenes.
Source: wikipedia
● Protects complex and sensitive objects from undesirable calling.
● Additional level for control data flow.
● Complex Proxy can be use as Service Stub.
TL;DR: If you need to control flow through part of system or service - add class
between that part that will be mocking functionality.

Decorator
● Allows behavior to be added to an individual object, either statically or dynamically,
without affecting the behavior of other objects from the same class.[1] The decorator
pattern is often useful for adhering to the Single Responsibility Principle, as it allows
functionality to be divided between classes with unique areas of concern.
Source: wikipedia
● Adding new functionality to already existing classes without changing code of that
classes.
● Recursive wrapping core objects with new functionalities.
● Strong SOLID.
TL;DR: If you want to add new features to already existing class - don’t change code of
that class but add new class and pass core class instance to it.

Decorator
● Proxy vs Decorator: Proxy creates instance of class within own object, Decorator
gets the class instance in constructor.

Composite
● Describes that a group of objects is to be treated in the same way as a single
instance of an object. The intent of a composite is to "compose" objects into tree
structures to represent part-whole hierarchies. Implementing the composite pattern
lets clients treat individual objects and compositions uniformly
Source: wikipedia
● Manage pool of objects with one objects with same interface.
● Creates tree structure.
● Solid hierarchy structure in code.
● DP Composite ≠ UML Composite
TL;DR: Use it when you need to create collection of one class objects.

Behavioral Design Patterns

Strategy
In computer programming, the strategy pattern (also known as the policy
pattern) is a software design pattern that enables an algorithm's behavior to be
selected at runtime. The strategy pattern
● defines a family of algorithms,
● encapsulates each algorithm, and
● makes the algorithms interchangeable within that family.
source: wikipedia.com

Strategy
https://github.com/domnikl/DesignPatternsPHP/tree/master/Behavioral/Strategy

Strategy
https://sourcemaking.com/design_patterns/strategy

Iterator
In object-oriented programming, the iterator pattern is a design pattern in
which an iterator is used to traverse a container and access the container's
elements. The iterator pattern decouples algorithms from containers; in some
cases, algorithms are necessarily container-specific and thus cannot be
decoupled.

Iterator
https://sourcemaking.com/design_patterns/iterator

Mediator
In software engineering, the mediator pattern defines an object that
encapsulates how a set of objects interact.
With the mediator pattern, communication between objects is encapsulated
with a mediator object. Objects no longer communicate directly with each
other, but instead communicate through the mediator. This reduces the
dependencies between communicating objects, thereby lowering the coupling.

Mediator

Recapitulation

Recapitulation
● What does Solid mean?
● What does Demeter law mean?
● How to work with creational design patterns?
● How to work with structural design patterns?
● How to work with behavioral design patterns?

xsolve.pl/career
Thank you for your time!

Xlab #2: wzorce projektowe

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Andere mochten auch

Andere mochten auch (6)

Ähnlich wie Xlab #2: wzorce projektowe

Ähnlich wie Xlab #2: wzorce projektowe (20)

Mehr von XSolve

Mehr von XSolve (15)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Xlab #2: wzorce projektowe