PHP best method to affect variables in a function

I'm playing around with hooking into functions, the hook will call the method of another object, what is the best way of changing the value $price in the parent function before it is returned?

function _product_price ($price,$taxable = true)
{
    $shop->_hook('PRODUCT_PRICE_BEFORE');
    $price = 100.00;
    $shop->_hook('PRODUCT_PRICE_AFTER');
    return number_format($price,2);
}

Thanks guys, would this be a suitable solution?

function _product_price ($price,$taxable = true)
{
    global $shop;
    $shop->_hook('PRODUCT_PRICE_BEFORE');
    $price = 100.00;
    $shop-&g开发者_运维技巧t;passedArgs['price'] = $price;
    $shop->_hook('PRODUCT_PRICE_AFTER');
    return number_format($shop->passedArgs['price'],2);
}
function _hook ()
{
    global $shop;
    $shop->passedArgs['price'] = 23.00;
    return;
}

Since you likely want to register arbitrary methods for hooks, have a look at

• Subject/Observer and
• Event Dispatcher

I'd pass the variables to the point either:

• as an array of references, (array('price' => &$price); would make any change to the $var['price'] variable in a function later on / deeper reflect in the 'in-scope' $price.
• set the variables to the point as an object-property and just pass the current observable object as a parameter.