Static Methods & Properties

Also Known As

TL;DR

Explanation

Static methods and properties belong to the class rather than an instance and are called with :: (ClassName::method()). They are appropriate for: pure utility functions (Math::clamp()), named constructors/factories (Money::fromFloat()), and singleton registries. However, static state is global state — it persists across test cases, cannot be easily mocked, and creates hidden dependencies. Static calls are hard to stub in tests without workarounds like Mockery's alias mocking. Prefer instance methods with dependency injection for anything stateful or replaceable; reserve static for genuinely stateless utilities.

Common Misconception

Why It Matters

Common Mistakes

• Using static methods for stateful operations — global state in static methods causes test pollution.
• Static factory methods that return a concrete type — cannot be overridden in subclasses without LSP violation.
• Calling static methods on $this inside a class — use self:: or static:: explicitly.
• Not distinguishing stateless utility statics (Math::round()) from stateful service statics (DB::query()) — the former is fine, the latter is problematic.

Code Examples

// Static method with global state — cannot be unit tested:
class Database {
    private static ?PDO $connection = null;
    public static function query(string $sql): array {
        return self::getConnection()->query($sql)->fetchAll();
    }
}
// Callers: Database::query() — tightly coupled, untestable without real DB

// Static methods: no instance state, utility/factory use cases
class Uuid {
    public static function v4(): string {
        return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
            mt_rand(0, 0xffff), mt_rand(0, 0xffff),
            mt_rand(0, 0xffff),
            mt_rand(0, 0x0fff) | 0x4000,
            mt_rand(0, 0x3fff) | 0x8000,
            mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
        );
    }
}
$id = Uuid::v4();

// Named constructors — static factory on a value object
readonly class Temperature {
    private function __construct(public float $celsius) {}
    public static function fromCelsius(float $c): self    { return new self($c); }
    public static function fromFahrenheit(float $f): self  { return new self(($f-32)*5/9); }
    public static function fromKelvin(float $k): self      { return new self($k-273.15); }
}

References

• ↗ https://www.php.net/manual/en/language.oop5.static.php

Tags

Related Terms