<?php readonly class Name implements Stringable { public function __construct( public string $value ) { if (strlen($value) === 0) { throw new ValueError("Name must be non-empty"); } } public function __toString(): string { return $this->value; } } readonly class User { public function __construct( public Name $name, // if we are receiving a Name instance, it just means that it's already a valid value! ) { } } $user1 = new User( new Name('Some valid name') ); echo $user1->name; // "Some valid name" $user2 = new User( new Name('') // kaboom );
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