Named Constructor Pattern

Also Known As

TL;DR

Explanation

PHP constructors have a single name (__construct) and cannot be overloaded. Named constructors are static methods that communicate intent: Money::fromCents(500), Money::fromDollars(5.00), DateRange::lastMonth(), User::createGuest(). They can return different subtypes, enforce invariants, or accept different input formats. Combined with a private constructor, they become the only way to instantiate the class — enforcing all construction passes through validated paths.

Common Misconception

Why It Matters

Common Mistakes

• Not making the constructor private when named constructors are the intended API — both paths remain available.
• Named constructors that accept the same parameters as the constructor — adds verbosity without clarity.
• Omitting validation in named constructors — they are the perfect place to enforce class invariants.
• Using static methods for everything instead of identifying which cases genuinely need named constructors.

Code Examples

// Ambiguous constructor — is 500 cents or dollars?
class Money {
    public function __construct(private int $amount, private string $currency) {}
}
new Money(500, 'USD'); // $500 or 500 cents? Who knows

// Named constructors — intent is explicit:
class Money {
    private function __construct(
        private readonly int $cents,
        private readonly string $currency,
    ) {}

    public static function fromCents(int $cents, string $currency): self {
        if ($cents < 0) throw new InvalidArgumentException('Amount cannot be negative');
        return new self($cents, $currency);
    }

    public static function fromDollars(float $dollars, string $currency): self {
        return new self((int) round($dollars * 100), $currency);
    }

    public static function zero(string $currency): self {
        return new self(0, $currency);
    }
}

References

• ↗ https://verraes.net/2014/06/named-constructors-in-php/

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