PSR Coding Style Knowledge (PSR-1, PSR-12)

Quick Reference

Standard	Focus	Key Rules
PSR-1	Basic Standard	Files, namespaces, class names
PSR-12	Extended Style	Formatting, keywords, visibility

PSR-1: Basic Coding Standard

1. Files

Rule	Requirement
Tags	MUST use `<?php` or `<?=` only
Encoding	MUST be UTF-8 without BOM
Side Effects	Files SHOULD declare symbols OR execute logic, not both

2. Namespaces and Classes

Rule	Requirement
Namespaces	MUST follow PSR-4 autoloading
Class Names	MUST be `StudlyCaps` (PascalCase)
Constants	MUST be `UPPER_CASE_WITH_UNDERSCORES`
Methods	MUST be `camelCase`

3. Side Effects Detection

php

// BAD: Mixing declarations and side effects
<?php
namespace App;

ini_set('display_errors', '1');  // Side effect!

class Logger { }

// GOOD: Separate files
// bootstrap.php
<?php
ini_set('display_errors', '1');
require 'vendor/autoload.php';

// Logger.php
<?php
declare(strict_types=1);

namespace App;

final readonly class Logger { }

PSR-12: Extended Coding Style

1. General

Rule	Requirement
PSR-1	MUST follow PSR-1
Indentation	MUST use 4 spaces (no tabs)
Line Length	SHOULD be ≤120 chars, MUST NOT hard wrap
Line Ending	MUST be Unix LF (`\n`)
Blank Line	MUST have one at end of file
Trailing Space	MUST NOT have trailing whitespace

2. Files

php

<?php

declare(strict_types=1);

namespace Vendor\Package;

use Vendor\Package\{ClassA as A, ClassB, ClassC as C};
use Vendor\Package\SomeNamespace\ClassD as D;

use function Vendor\Package\{functionA, functionB, functionC};
use const Vendor\Package\{ConstantA, ConstantB, ConstantC};

final readonly class ClassName extends ParentClass implements
    InterfaceA,
    InterfaceB,
    InterfaceC
{
    // class body
}

3. Keywords and Types

Rule	Requirement
Keywords	MUST be lowercase (`true`, `false`, `null`)
Type Declarations	MUST be lowercase (`int`, `string`, `bool`)
Short Forms	MUST use `bool`, `int` (not `boolean`, `integer`)

4. Classes, Properties, Methods

php

<?php

declare(strict_types=1);

namespace App\Domain\Entity;

use App\Domain\ValueObject\Email;
use App\Domain\ValueObject\UserId;

final readonly class User
{
    public function __construct(
        private UserId $id,
        private Email $email,
        private string $name,
        private bool $isActive = true,
    ) {
    }

    public function getId(): UserId
    {
        return $this->id;
    }

    public function activate(): self
    {
        return new self(
            $this->id,
            $this->email,
            $this->name,
            true,
        );
    }
}

5. Control Structures

php

<?php

// if-elseif-else
if ($expr1) {
    // if body
} elseif ($expr2) {
    // elseif body
} else {
    // else body
}

// switch
switch ($expr) {
    case 0:
        echo 'First case';
        break;
    case 1:
        echo 'Second case';
        // no break - intentional fall-through
    default:
        echo 'Default case';
        break;
}

// match (PHP 8.0+)
$result = match ($expr) {
    0 => 'First',
    1, 2 => 'Second or third',
    default => 'Other',
};

// while
while ($expr) {
    // body
}

// for
for ($i = 0; $i < 10; $i++) {
    // body
}

// foreach
foreach ($iterable as $key => $value) {
    // body
}

// try-catch-finally
try {
    // try body
} catch (FirstThrowableType $e) {
    // catch body
} catch (OtherThrowableType | AnotherThrowableType $e) {
    // multi-catch body
} finally {
    // finally body
}

6. Operators

php

<?php

// Binary operators: space before and after
$sum = $a + $b;
$concat = $string1 . $string2;
$result = $condition ? $valueIfTrue : $valueIfFalse;

// Unary operators: no space
$i++;
--$j;
$negated = !$bool;

// Type casting: no space after cast
$intValue = (int) $floatValue;
$stringValue = (string) $intValue;

7. Closures and Arrow Functions

php

<?php

// Closure
$closure = function (int $arg1, int $arg2) use ($var1, $var2): int {
    return $arg1 + $arg2 + $var1 + $var2;
};

// Long argument list
$longClosure = function (
    int $argument1,
    string $argument2,
    bool $argument3,
) use (
    $staticVar1,
    $staticVar2,
): bool {
    // body
};

// Arrow function (PHP 7.4+)
$multiply = fn(int $a, int $b): int => $a * $b;

8. Anonymous Classes

php

<?php

$instance = new class extends ParentClass implements SomeInterface {
    use SomeTrait;

    public function __construct(
        private readonly int $value,
    ) {
    }
};

Detection Patterns

PSR-1 Violations

bash

# Side effects in class files (functions like echo, print, header, etc.)
grep -rn "^[[:space:]]*\(echo\|print\|header\|session_start\|ini_set\)" --include="*.php" src/

# Non-StudlyCaps class names
grep -rn "^class [a-z]" --include="*.php" src/
grep -rn "^class [A-Z][a-z]*_" --include="*.php" src/

# Non-camelCase method names
grep -rn "function [A-Z]" --include="*.php" src/
grep -rn "function [a-z]*_[a-z]" --include="*.php" src/

PSR-12 Violations

bash

# Tab characters instead of spaces
grep -rn $'\t' --include="*.php" src/

# Trailing whitespace
grep -rn "[[:space:]]$" --include="*.php" src/

# Long keywords (boolean instead of bool)
grep -rn "boolean\|integer" --include="*.php" src/

# Missing space after keywords
grep -rn "\(if\|for\|foreach\|while\|switch\|catch\)(" --include="*.php" src/

# Opening brace on wrong line for classes
grep -rn "^class.*{$" --include="*.php" src/

PHP_CodeSniffer Configuration

xml

<?xml version="1.0"?>
<ruleset name="PSR-12">
    <description>PSR-12 coding standard</description>
    <rule ref="PSR12"/>

    <file>src</file>
    <file>tests</file>

    <exclude-pattern>vendor/*</exclude-pattern>

    <arg name="colors"/>
    <arg value="sp"/>
</ruleset>

PHP-CS-Fixer Configuration

php

<?php

declare(strict_types=1);

use PhpCsFixer\Config;
use PhpCsFixer\Finder;

$finder = Finder::create()
    ->in([
        __DIR__ . '/src',
        __DIR__ . '/tests',
    ])
    ->name('*.php');

return (new Config())
    ->setRiskyAllowed(true)
    ->setRules([
        '@PSR12' => true,
        '@PHP84Migration' => true,
        'declare_strict_types' => true,
        'final_class' => true,
        'class_attributes_separation' => [
            'elements' => ['method' => 'one'],
        ],
        'ordered_imports' => [
            'sort_algorithm' => 'alpha',
            'imports_order' => ['class', 'function', 'const'],
        ],
        'no_unused_imports' => true,
        'trailing_comma_in_multiline' => [
            'elements' => ['arguments', 'arrays', 'parameters'],
        ],
    ])
    ->setFinder($finder);

Antipatterns

Violation	PSR	Severity	Fix
Mixed declarations and side effects	PSR-1	CRITICAL	Separate into bootstrap file
snake_case class names	PSR-1	CRITICAL	Rename to StudlyCaps
Tabs for indentation	PSR-12	WARNING	Convert to 4 spaces
Boolean/integer type hints	PSR-12	WARNING	Use bool/int
Missing strict_types	-	WARNING	Add declaration
Opening brace on same line	PSR-12	INFO	Move to next line
Trailing whitespace	PSR-12	INFO	Remove whitespace

Integration with DDD

Domain Layer

php

<?php

declare(strict_types=1);

namespace App\Domain\User\ValueObject;

// PSR-12 compliant Value Object
final readonly class Email
{
    private function __construct(
        private string $value,
    ) {
    }

    public static function fromString(string $email): self
    {
        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            throw new InvalidEmailException($email);
        }

        return new self($email);
    }

    public function toString(): string
    {
        return $this->value;
    }
}

Application Layer

php

<?php

declare(strict_types=1);

namespace App\Application\User\UseCase;

use App\Application\User\Command\CreateUserCommand;
use App\Domain\User\Entity\User;
use App\Domain\User\Repository\UserRepositoryInterface;

// PSR-12 compliant Use Case
final readonly class CreateUserHandler
{
    public function __construct(
        private UserRepositoryInterface $userRepository,
    ) {
    }

    public function __invoke(CreateUserCommand $command): void
    {
        $user = User::create(
            $command->email,
            $command->name,
        );

        $this->userRepository->save($user);
    }
}

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PSR Coding Style Knowledge (PSR-1, PSR-12)

Quick Reference

PSR-1: Basic Coding Standard

1. Files

2. Namespaces and Classes

3. Side Effects Detection

PSR-12: Extended Coding Style

1. General

2. Files

3. Keywords and Types

4. Classes, Properties, Methods

5. Control Structures

6. Operators

7. Closures and Arrow Functions

8. Anonymous Classes

Detection Patterns

PSR-1 Violations

PSR-12 Violations

PHP_CodeSniffer Configuration

PHP-CS-Fixer Configuration

Antipatterns

Integration with DDD

Domain Layer

Application Layer

See Also