Re: __clone() implementation

Hello Stephane, you're right $that must be available in the derived __clone(). Thursday, January 22, 2004, 3:37:11 PM, you wrote: > I'm currently using PHP4 and I'm evaluating PHP5 for its new exciting features. > I have some remarks, split into distinct posts. > The first one is about the current implementation of __clone(): > * a derived __clone() can't call parent::__clone() because $that is > only declared for the first __clone() call. So a derived __clone() has to > include the code of its parent's __clone(). It's not only bad programming, > but it can't work when a parent implements private members. > * when a class implements __clone(), all its derived classes have also > to implement it to transfer their own members. > There are a several possibilities to get round the first point, but in > order to also simplify __clone() implementation, here is a way it could be > implemented, close to __construct() implementation: > * the system firstly does a bit for bit copy of the source object, > * then it calls __clone() (which at worst does nothing, if no class implements it), > * __clone() accesses members using $this to handle those (and only > those) that need particular actions, > * this is the responsibility of a derived __clone() to call (or not) parent::__clone(). > Advantages: > * same behaviour as __construct(), except that $this is already initialized, > * it guaranties that all members will be transfered, by reference for objects, by copy for the > others, > * __clone() just needs to be implemented to handle members that need particular actions, > * derived classes do not need to implement __clone() when one of its parents does, > * no more need of $that. > In terms of performance, I don't think this implementation is bad, > because a bit for bit copy is certainly faster than an interpreted > member-to-member transfer, except if all members have to be handled in a > particular way. > I also consider the __clone() implementation not coherent with its calling syntax. > Indeed "$newObj = $obj->__clone();" lets think of an implementation like this: > <? > class Foo { > function __clone() { > $o = new Foo($this->..., $this->...); > $o->...; // eventually > return $o; > } > } ?>> > Because __clone() is considered as a copy constructor, it could be > implemented in a similar way as for object construction, for example: > "$newObj = clone $obj;", "clone" being a language keyword. > Regards, > Stephane -- Best regards, Marcus mailto:helly@php.net