them in the manual at echecs16.info Later on, when we cover Design Patterns, I'll talk about the magic methods a bit more. For now, here's a. Author Jason E. Sweat's book php|architect's Guide to PHP Design The ValueObject Pattern; The Factory Pattern; The Singleton Pattern; The. Selection from Mastering PHP Design Patterns [Book] Learn about advanced design patterns in PHP 7; Understand enhanced architectural patterns; Learn to This comprehensive guide will show you how to achieve better organization statements and switch statements with polymorphism or the Strategy Pattern.
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Guide to. PHP Design Patterns. A Practical Approach to Design Patterns The term “design pattern” was originally coined in the field of architecture. php|architect's Guide to PHP Design Patterns - Treinamento. Pages · · MB Core PHP Programming Using PHP to Build Dynamic Web Sites. It continues through a host of Design Patterns with code examples and using Observer Design Pattern ○ How to plan application architecture using .. Intermediate programmers may need to reference the PHP manual from time to time.
Defines a new operation to a class without change Criticism The concept of design patterns has been criticized by some in the field of computer science. Targets the wrong problem The need for patterns results from using computer languages or techniques with insufficient abstraction ability. Under ideal factoring, a concept should not be copied, but merely referenced. But if something is referenced instead of copied, then there is no "pattern" to label and catalog. Paul Graham writes in the essay Revenge of the Nerds. Peter Norvig provides a similar argument.
Collection of implementation examples Factory One of the most commonly used design patterns is the factory pattern. In this pattern, a class simply creates the object you want to use. There are two possible benefits to building your code this way; the first is that if you need to change, rename, or replace the Automobile class later on you can do so and you will only have to modify the code in the factory, instead of every place in your project that uses the Automobile class.
The second possible benefit is that if creating the object is a complicated job you can do all of the work in the factory, instead of repeating it every time you want to create a new instance. The example code used here is so simple that a factory would simply be adding unneeded complexity.
However if you are making a fairly large or complex project you may save yourself a lot of trouble down the road by using factories. Factory pattern on Wikipedia Singleton When designing web applications, it often makes sense conceptually and architecturally to allow access to one and only one instance of a particular class. The singleton pattern enables us to do this. A new instance is created via late static binding in the static creation method getInstance with the keyword static.
This allows the subclassing of the class Singleton in the example. The singleton pattern is useful when we need to make sure we only have a single instance of a class for the entire request lifecycle in a web application. For instance, sites built using older versions of Wordpress or Moodle are heavily procedural; whereas, sites built using Laravel are completely OOP.
Imperative programming treats a computer program as merely a sequence of top-to-bottom statements that change the state of the system in order to compute a result.
Suppose you need to square all of the numbers in an array.
This is the most common way of writing this code and most likely will be your first approach to tackling this problem. Declarative programming, on the other hand, separates program description from evaluation.
It focuses on the use of expressions to describe what the logic of a program is or what output would look like without necessarily specifying its control flow or state changes. Once you employ this vocabulary to concoct the instructions subroutines, functions, procedures, etc that make up your program, the PHP runtime translates this higher level of abstraction into regular PHP code: Shifting to a functional approach to tackle this same task, you only need to be concerned with applying the correct behavior at each element and cede control of looping to other parts of the system.
Notice a trend?
Consider this example. Suppose we also needed to add all of the values within the array. Also, standard loops are not reusable artifacts, only when they are abstracted within functions.
Coding with immutable variables has many benefits such as: One of the main causes of bugs in software is when the state of an object inadvertently changes, or its reference becomes null. Immutable objects can be passed around to any function and their states will always remain the same. You can count on having the peace mind that state is only permitted to grow but never change.
Immutable data structures are important in shared memory multithreaded applications.
Now, whether designing for parallelism or not, stateless objects is a widely used pattern seen in many common PHP deployments. For example, as a best practice, Symfony services or service objects should always be stateless. Because define is a function, you can use it to create constants with arbitrary expressions and also declare them to be case insensitive if you wish to do so.
But you can get close to achieving stateless programs, just like those Symfony services we spoke about earlier, using pure functions. Pure functions fix side effects Functional programming is based on the premise that you will build immutable programs based on pure functions as the building blocks of your business logic.
A pure function has the following qualities: It depends only on the input provided and not on any hidden or external state that may change during its evaluation or between calls.
This includes your Laravel Active Record objects, for example. Operations in DAOs always cause side effects because their sole purpose is to interact with an external resource, the database. Programming with immutability can feel rather strange at first.
This is a very natural thing for us to do. This is not only considered bad practice from a functional point of view, but also a bit frowned upon in modern PHP applications. Generally speaking, functions have side effects when reading from or writing to external resources. Matters get worse, when this state is shared: In this case, doWork and doMoreWork are very tightly coupled.
This coupling means that you necessarily need to invoke doWork before calling doMoreWork, always in that order. Hence, you lose the autonomy of these functions and make them harder to unit test in isolation.
Side effects create a temporal coupling or dependency, which means the execution of one can determine the outcome of the next.
The result of doMoreWork is reliant on doWork. In functional programming, functions should behave like reusable artifacts that can be evaluated in any order and continue to yield correct results.
Not all side effects are this obvious. Some of them are embedded into language level functions. Indeed, pure functions can be very hard to use in a world full of dynamic behavior and mutation— the real world. This is a simple example, of course, but this level of reasoning can be taken to functions of any complexity.
Generally, the goal is to create functions that do one thing and combine them together instead of creating large monolithic functions. Referential Transparency We can take the notion of purity a step further. In functional programming, we redefine what it means to create a function. In a sense we go back to basics, to the maths, and treat functions as nothing more than a mapping of types.
In this case, its input types arguments to its output type return value.
You can imagine that A and B are sets that represent the domain and the codomain of a function, respectively. For instance, the type int is analogous to the set of all integers Z. Functions that return the same values given the same input always, resembling this mathematical property, are known as referentially transparent RT.
A RT function can always be directly substituted or replaced for its computed value into any expression without altering its meaning. This conclusion can only be reached when there are no side effects in your code. Using RT functions we derive the following corollary. This makes your code not only easier to test, but also allows you to reason about entire programs much easier. Referential transparency also known as equational correctness is inherited from math, but functions in programming languages behave nothing like mathematical functions; so achieving referential transparency is strictly on us, especially in a non-pure functional language such as PHP.
The benefit of doing is is that when your individual functions are predictable, the sum of the parts is predictable and, hence, much easier to reason about, maintain, and debug, and especially test. By now you realize why pure functions are the pillar of FP, but we have one more concept to introduce. If pure functions are the pillars, then composition is the base or the glue that makes up the entire system.
A look into functional decomposition At the core, functional programming is effectively the interplay between decomposition breaking programs into small pieces and composition glueing the pieces back together.
It is this duality that makes functional programs modular and so effective. Thinking functionally typically begins with decomposition or learning to break up a particular task into logical subtasks functions. The idea is that you learn to decompose programs into the simplest reusable units of composition.
In short, they must agree on their exposed contracts, which is very similar to the Coding to Interfaces OO design principle. A practical observation and not a formal concept indicates that the lower the number of function parameters, the simpler the function tends to be. This process is essentially what compose does.
This is essentially the same coding to interfaces but at a much lower level of granularity. To sum up, what is functional programming? This will set the stage for developing data flows in chapter 3. So stay tuned! Higher-order PHP I mentioned in chapter 1 that functional programming is not a new framework, library, or design pattern. However, paradigms by themselves are just abstract concepts that need the right host language to become a reality.
And, yes! PHP is that language. The goal of this chapter is to teach you how to use functions in a very different way—the functional way. Both are intimately related, as the ability of a language artifact to be passed in as an argument or returned from a functions hinges on it being considered just another object.
This also means, of course, that functions can be assigned to variables. Assigning to a variable This means that you should be able to treat a function just like any other type of object.