A preliminary study on PHP PSR2 and PSR4 specifications

Initial exploration of PHP PSR2 and PSR4 specifications

Introduction:
In the process of writing PHP code, it is very important to follow certain coding specifications. Good coding standards can improve the readability and maintainability of code and facilitate teamwork. PHP has a series of coding specifications, of which PSR2 and PSR4 are the two most widely used specifications. This article will focus on the PSR2 and PSR4 specifications and illustrate how to follow these specifications through specific code examples.

1. PSR2 specification
The PSR2 specification mainly focuses on the readability and consistency of PHP code. Here are some common specification requirements:

1. Indentation
2. Use 4 spaces for indentation and no tabs.
3. Use 4 spaces for one indentation level.
4. File header comments
5. Each PHP file should contain appropriate file header comments to describe the purpose, author, creation date and other information of the file.
6. Line break
7. Wrap the line after the statement ends, keeping each line to no more than 80 characters.
8. There should be a blank line between methods to improve the readability of the code.
9. Functions and methods
10. Function names and method names should use camel case naming, that is, the first letter is lowercase, and the first letter of subsequent words is capitalized.
11. The left parenthesis of functions and methods should be on the same line as the function or method name, and the right parenthesis should be on a separate line, aligned with the left parenthesis of the function or method.
12. Space
13. There should be a space before and after operators (such as =, , -, etc.).
14. There should be a space after the keywords of the control structure (such as if, for, while, etc.).

The following is a sample code that complies with the PSR2 specification:

<?php
namespace MyApp;

class Calculator
{
    public function add($a, $b)
    {
        return $a + $b;
    }
    
    public function subtract($a, $b)
    {
        return $a - $b;
    }
}

$calculator = new Calculator();
$result = $calculator->add(2, 3);
echo $result;

2. PSR4 specification
The PSR4 specification mainly focuses on PHP's namespace and automatic loading. The following are some common specification requirements:

1. Namespace and class names
2. Use lowercase letters for namespaces, and use "" as a delimiter.
3. Class names use camel case naming, that is, the first letter of each word is capitalized.
4. Directory structure
5. The class should be consistent with the directory structure, and each part of the namespace corresponds to a subdirectory.
6. The extension of the class file should be .php.
7. Auto-loading
8. Use Composer to manage dependencies and auto-loading functions.
9. Configure PSR4 class loading rules in the composer.json file.

The following is a sample code that complies with the PSR4 specification:

(Set the mapping relationship between namespace and class in the composer.json file)

{
    "autoload": {
        "psr-4": {
            "MyApp\": "src/"
        }
    }
}

(In Calculator class defined in src/Calculator.php)

<?php
namespace MyApp;

class Calculator
{
    public function add($a, $b)
    {
        return $a + $b;
    }
    
    public function subtract($a, $b)
    {
        return $a - $b;
    }
}

(Use automatic loading in index.php)

<?php
require_once 'vendor/autoload.php';

use MyAppCalculator;

$calculator = new Calculator();
$result = $calculator->add(2, 3);
echo $result;

Conclusion:
Following the PSR2 and PSR4 specifications can improve the reliability of PHP code Readability, maintainability and scalability. During the development process, we should actively adopt these specifications and check whether the code conforms to the specifications by using tools such as CodeSniffer. This helps us write better PHP code.

We hope that through the introduction and sample code of this article, readers will have a preliminary understanding of the PSR2 and PSR4 specifications and be able to apply these specifications in actual projects. Only by constantly learning and practicing and constantly improving your coding level can you become an excellent PHP developer.

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