php object caching within constructor

Question

I'd like to be able to use transparent (poor mans) caching of objects by using the constructor and not some factory method.

$a = new aClass(); should check if this objects exists in cache and if it doesn't exist create it and add it to the cache.

Some pseudo-code:

class aClass {
    public function __construct($someId) {
        if (is_cached($someId) {
            $this = get_cached($someId);
        } else {
            // do stuff here
            set_cached($someId, $this);
        }
    }
}

Unfortunately, this is impossible because you can't redefine $this in php.

Any suggestions?

First, I want transparency and second I don't want to rewrite hundreds of thousands lines of code. — Bernd Goldschmidt
– Bernd Goldschmidt, Commented Mar 7, 2012 at 10:16

Gordon · Accepted Answer · 2012-03-07 09:56:47Z

5

This will not work because ctors dont return and you cannot redefine $this.

You can use a static factory method instead:

class Foo
{
    protected static $instances = array();

    public function getCachedOrNew($id)
    {
        if (!isset(self::$instances[$id])) {
            self::$instances[$id] = new self;
        }
        return self::$instances[$id];
    }
}

$foo = Foo::getCachedOrNew(1);
$foo->bar = 1;
$foo = Foo::getCachedOrNew(1);
echo $foo->bar; // 1

Another alternative would be to use a Dependency Injection Container (DIC) that can manage objects instances. Have a look at The Symfony Componenent DIC. for this.

edited Mar 7, 2012 at 9:56

answered Mar 7, 2012 at 9:32

Gordon

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1 Comment

Bernd Goldschmidt Over a year ago

As I mentioned, I don't want to use a factory method to create the object, I want transparent caching. But I looks like this is not possible with php.

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