<?php abstract class StringWrapper { protected function __construct(readonly public string $value) {} abstract public static function parse(string $raw): self; } class Email extends StringWrapper { public static function parse(string $raw): self { str_contains($raw, '@') or throw new InvalidArgumentException(); return new self($raw); } } class User { public function __construct(readonly public Email $email) {} // Constructors should be strict, use factory methods for a friendly API public static function make(string|Email $email): self { $email instanceof Email or $email = Email::parse($email); return new self($email); } } $user = new User(Email::parse("dude@la.us")); $user = User::make("walter@la.us"); // $user = User::make("donnie"); // throws
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