East oriented account transfert

gistfile1.php

<?php

namespace east;

class amount
{
	private
		$value
	;

	function __construct($value)
	{
		$this->value = $value;
	}

	function __get($property)
	{
		return $property === 'value' ? $this->value : null;
	}
}

class balance
{
	private
		$amount
	;

	function __construct(amount $amount)
	{
		$this->amount = $amount;
	}

	function add(amount $amount)
	{
		return new self(new amount($this->amount->value + $amount->value));
	}

	function sub(amount $amount)
	{
		return new self(new amount($this->amount->value - $amount->value));
	}
}

class account
{
	private
		$balance
	;

	function __construct(balance $balance)
	{
		$this->balance = $balance;
	}

	function add(amount $amount)
	{
		$this->balance = $this->balance->add($amount);

		return $this;
	}

	function remove(amount $amount)
	{
		$this->balance = $this->balance->sub($amount);

		return $this;
	}
}

class transaction
{
	function __construct(amount $amount, account $from, account $to)
	{
		$this->amount = $amount;
		$this->to = $to;
		$this->from = $from;
	}

	function execute()
	{
		$this->from->remove($this->amount);
		$this->to->add($this->amount);

		return $this;
	}
}

$to = new account(new balance(new amount(10)));
$from = new account(new balance(new amount(5)));

(new transaction(new amount(2), $from, $to))->execute();
var_dump($from, $to);

(new transaction(new amount(2), $to, $from))->execute();
var_dump($from, $to);