# PHP PSR Standards

**PSR** stands for **PHP Standards Recommendations**. These standards are published by the PHP Framework Interop Group (PHP-FIG) to improve interoperability between PHP frameworks and libraries.

---

## 1. PSR-1: Basic Coding Standard
This standard outlines the basic rules to ensure a high level of technical interoperability between shared PHP code.

*   Files MUST use only `<?php` and `<?=`.
*   Files MUST use only UTF-8 without BOM.
*   Class names MUST be declared in `StudlyCaps`.
*   Method names MUST be declared in `camelCase`.
*   Constants MUST be declared in all upper case with underscore separators.

## 2. PSR-4: Autoloading Standard
PSR-4 describes a specification for autoloading classes from file paths. It replaces the older PSR-0 standard.

*   It maps namespaces to file system directories.
*   Example: `\Namespace\ClassName` maps to `path/to/project/src/ClassName.php`.
*   This is the standard used by **Composer**.

```json
// composer.json
"autoload": {
    "psr-4": {
        "App\\": "src/"
    }
}
```

## 3. PSR-12: Extended Coding Style
PSR-12 extends and replaces PSR-2. It provides a coding style guide for projects.

*   Code MUST use 4 spaces for indenting, not tabs.
*   Lines SHOULD NOT be longer than 120 characters.
*   Opening braces for classes MUST go on the next line.
*   Opening braces for methods MUST go on the next line.
*   Visibility (public, protected, private) MUST be declared on all properties and methods.

```php
<?php

namespace Vendor\Package;

class ClassName
{
    public function fooBarBaz($arg1, &$arg2, $arg3 = [])
    {
        // method body
    }
}
```

[[programming/php/php]] [[programming/php/php-composer]]