Nested/Inner classes playground

person.php

<?php

class Person
{
  private interface Name
  {
    public function __construct(string $name);
    public function __toString() : string;
  }
  
  private class FirstName implements self\Name
  {
    private $name;
    
    public function __construct(string $name) {
      // validation
      if (strlen($name) < 3) {
        throw new InvalidargumentException("First name should have min 3 letters long, given: {$name}");
      }
      $this->name = $name;
    }
    
    public function __toString() : string {
      return $this->name;
    }
  }
  
  private class SecondName implements self\Name
  {
    private $name;
    
    public function __construct(string $name) {
      // it would be reasonable to have access to owning object but `parent` already taken by super class
      // shouldn't `parent` be renamed to `super`!
      // then `$parent` could be owning object `$this`
      if (is_null($parent->firstName)) {
        throw new RuntimeException("It is impossible to have second name without firstname");
      }
      // validatiojn
      if (strlen($name) < 1) {
        throw new InvalidargumentException("Second name should have min 1 letter long, given: {$name}");
      }
      $this->name = $name;
    }
    
    public function __toString() : string
    {
      return $this->name;
    }
  }
  
  /** @var self\FirstName */
  private $firstName;
  /** @var self\SecondName */
  private $secondName;
  
  public function __construct(string $fname, string $sname) {
    $this->firstName = new $this\FirstName($fname);
    $this->secondName = new $this\SecondName($sname);
  }
  
  public function getName() : string {
    return "{$this->firstName} {$this->secondName}";
  }
}

stock.php

<?php

class Stock implements IteratorAggregate
{
  public class Option
  {
    private $name;
    private $value;
    
    public function __construct(string $name, int $value)
    {
      if (strlen($name) < 3) {
        throw new InvalidArgumentException("Stock option name requires min. 3 letters long, given: {$name}");
      }
      if ($value <= 0) {
        throw new InvalidArgumentException("Stock option must have positive value, given: {$value}");
      }
      $this->name = $name;
      $this->value = $value;
      // if there were access to owning `$this` by `$parent`
      // then could automatically add to options table
      $parent->options[] = $this;
    }
  }
  
  private $options = [];
  
  public function getIterator() {
    return new ArrayIterator($this->options);
  }
}

$stock = new Stock();
$option = new $stock\Option("MAD", 1500);
var_dump($stock);
// class Stock#1 (1) {
//   private $options =>
//   array(1) {
//     [0] =>
//     class Stock#1Option#2 (2) {
//       private $name =>
//       string(3) "MAD"
//       private $value =>
//       int(1500)
//     }
//   }
// }

$incorectlyNamedOption = new $stock\Option("a", 1);
// InvalidArgumentException: Stock option name requires min. 3 letters long, given: a

$incorectValueOption = new $stock\Option("ORA", -1);
// InvalidArgumentException: Stock option must have positive value, given: -1"