Custom setter

If a field requires additional processing during its initialization, you can define a mutator. To define a mutator, define a set{Attribute}Attribute method on your class, where {Attribute} is the studly-cased name of the property you wish to access. This mutator will be automatically called when we attempt to set the value of the real_address attribute on the model:

class UserDTO
{
    public int $id;
    public string $real_address;

    public function setRealAddressAttribute(string $value)
    {
        $this->real_address = strtolower($value);
    }
}