PHP Code Style (PSR Standards)

PSR standards are shared writing rules for PHP code, like agreeing to use the same spelling and layout in a group story. They make code from different people easy to read.

In this page:

Introduction to PSR Standards
PSR-12 Code Style
PSR-4 Autoloading
PSR-3 Logger Interface
PSR-7 HTTP Messages

Introduction to PSR Standards

PSRs (PHP Standard Recommendations) are community-agreed conventions from the PHP-FIG group covering everything from code formatting to interfaces, letting independently written packages interoperate smoothly.

Example: Introduction to PSR Standards

php

<?php
// Print "PSRs are community-agreed conventions from PHP-FIG for interoperability" to the output
echo "PSRs are community-agreed conventions from PHP-FIG for interoperability";
?>

PSR-12 Code Style

PSR-12 defines exact rules for spacing, brace placement, and method signatures, so code from different developers or packages reads consistently instead of everyone following their own personal style.

Example: PSR-12 Code Style

php

<?php
// Define the class `UserController`
class UserController
{
    // Define the function `show` taking `int $id`
    public function show(int $id): void
    {
        // Print `$id` to the output
        echo $id;
    }
}
// Print "Consistent spacing and brace placement, regardless of author" to the output
echo "Consistent spacing and brace placement, regardless of author";
?>

PSR-4 Autoloading

PSR-4 standardizes how a namespace maps to a folder structure, which is the exact convention Composer's autoloader relies on to find and load classes without any manual configuration per package.

Example: PSR-4 Autoloading

php

<?php
// namespace App\Models; --> maps to src/Models/ per composer.json's psr-4 config
echo "Namespace structure mirrors folder structure";
?>

PSR-3 Logger Interface

PSR-3 defines a standard logging interface (with methods like info(), warning(), error()), so a library can accept 'any PSR-3 logger' and work with Monolog, a custom logger, or anything else that implements it.

Example: PSR-3 Logger Interface

php

<?php
// Define the interface `LoggerInterface` describing required methods
interface LoggerInterface {
    // Define the function `info` taking `$message`
    function info($message);
    // Define the function `warning` taking `$message`
    function warning($message);
    // Define the function `error` taking `$message`
    function error($message);
}
// Define the class `SimpleLogger`, implementing `LoggerInterface`
class SimpleLogger implements LoggerInterface {
    // Define the function `info` taking `$message`
    function info($message) { echo "INFO: $message"; }
    // Define the function `warning` taking `$message`
    function warning($message) { echo "WARNING: $message"; }
    // Define the function `error` taking `$message`
    function error($message) { echo "ERROR: $message"; }
}
(new SimpleLogger())->info("App started");
?>

PSR-7 HTTP Messages

PSR-7 standardizes how HTTP requests and responses are represented as objects, which is what allows middleware from different packages to be composed together in frameworks that follow the standard.

Example: PSR-7 HTTP Messages

php

<?php
// interface RequestInterface { function getMethod(); function getUri(); }
echo "Standardizes HTTP requests/responses as objects across frameworks";
?>

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