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Date: Wed, 16 Nov 2011 09:11:02 +0000
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To: Rasmus Schultz <rasmus@mindplay.dk>
Cc: Stefan Marr <php@stefan-marr.de>, internals@lists.php.net
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Subject: Re: [PHP-DEV] some notes about traits
From: rquadling@gmail.com (Richard Quadling)

On 16 November 2011 00:17, Rasmus Schultz <rasmus@mindplay.dk> wrote:
> Here's a better example of something useful that actually works:
>
> =C2=A0trait Accessors
> =C2=A0{
> =C2=A0 =C2=A0public function __get($name)
> =C2=A0 =C2=A0{
> =C2=A0 =C2=A0 =C2=A0return $this->{'get'.$name}();
> =C2=A0 =C2=A0}
>
> =C2=A0 =C2=A0public function __set($name, $value)
> =C2=A0 =C2=A0{
> =C2=A0 =C2=A0 =C2=A0$this->{'set'.$name}($value);
> =C2=A0 =C2=A0}
> =C2=A0}
>
> =C2=A0class OrderLine
> =C2=A0{
> =C2=A0 =C2=A0use Accessors;
>
> =C2=A0 =C2=A0public $price;
> =C2=A0 =C2=A0public $amount;
>
> =C2=A0 =C2=A0public function getTotal()
> =C2=A0 =C2=A0{
> =C2=A0 =C2=A0 =C2=A0return $this->price * $this->amount;
> =C2=A0 =C2=A0}
> =C2=A0}
>
> =C2=A0$line =3D new OrderLine;
>
> =C2=A0$line->price =3D 20;
> =C2=A0$line->amount =3D 3;
>
> =C2=A0echo "Total cost: ".$line->total;

I like that example. It shows, at a fairly simple level, the ability
to compose a class from potentially multiple traits.

Putting the __magic_methods in a trait, what a great idea. This
mechanism is allows for all sorts of easy to expand ideas.

You _COULD_ use this trait to implement discrete getters and setters ...

<?php
/**
 * Trait to provide setter and getter functionality
 * with an exception for any missing method.
 */
trait Accessors
	{
	public function __get($name)
		{
		if (method_exists($this, 'get' . $name))
			{
			return $this->{'get' . $name}();
			}
		elseif (property_exists($this, $name))
			{
			return $this->{$name};
			}
		else
			{
			throw new Exception("Cannot retrieve value of '$name'.");
			}
		}

	public function __set($name, $value)
		{
		if (method_exists($this, 'set' . $name))
			{
			$this->{'set' . $name}($value);
			}
		elseif (property_exists($this, $name))
			{
			$this->{$name} =3D $value;
			}
		else
			{
			throw new Exception("Cannot set value for '$name'.");
			}
		}
	}

/**
 * @property float $price
 * @property float $amount
 * @property float $tax
 * @property-readonly float $total
 */
class OrderLine
	{
	use Accessors;

	protected $price;
	protected $amount;
	protected $tax;

	public function getTotal()
		{
		return $this->price * $this->amount * (1 + ($this->tax / 100));
		}

	protected function getPrice()
		{
		return $this->price;
		}

	protected function getAmount()
		{
		return $this->amount;
		}

	protected function setPrice($price)
		{
		$this->price =3D $price;
		}

	protected function setAmount($amount)
		{
		$this->amount =3D $amount;
		}
	}

$line =3D new OrderLine;

$line->price =3D 20;
$line->amount =3D 3;
$line->tax =3D 10;

echo "Total cost: ".$line->total;
?>

outputs ...

Total cost : 66

So, the actual methods are hidden from public, but a developer can
extend the class to add additional processing.

Interestingly, I've used property_exists to expose public access to
protected properties. I suppose that is always possible. Bad design
really. I would guess you wouldn't mix the different access mechanisms
(public/protected/private, __get/__set, getter()/setter()).

Richard.


--=20
Richard Quadling
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