Domain-Driven Design in PHP

Currency and Money Example

The Currency and Money Value Objects are probably the most used examples for explaining Value Objects, thanks to the Money pattern. This design pattern provides a solution for modeling a problem that avoids a floating-point rounding issue, which in turn allows for deterministic calculations to be performed.

In the real world, a currency describes monetary units in the same way that meters and yards describe distance units. Each currency is represented with a three-letter uppercase ISO code:

class Currency {     private $isoCode;    public function __construct($anIsoCode)    {        $this->setIsoCode($anIsoCode);    }    private function setIsoCode($anIsoCode)    {        if (!preg_match('/^[A-Z]{3}$/', $anIsoCode)) { throw new InvalidArgumentException(); ...