Proposal: new magic methods for Object references.

2013/3/19 Matīss Roberts Treinis mrtreinis@gmail.com:

Proposal:

Two additional magic methods for PHP objects -

__refer(void):

Refer method is called whenever object's identifier is assigned to
variable, if such method is present.
Example:

$foo = new Bar;
$bar = $foo; //__refer invoked

Return values: null to proceed by assigning the variable to objects
identifier. Any other value returned would be assigned to variable
which is to hold the reference in case of null.

__unrefer($var):

Unrefer method would be called whenever object's identifier is about
to be replaced by anything else and would hold that something else as
argument.
Example:

$foo = new Bar;
$foo = false; //__unrefer invoked with false as argument

Return values: null to proceed with default by replacing value, false
to not to replace value and keep the reference in variable.

Real life use sample:

class SomeObject{
protected $count;
function __refer(){
$this->count++;
}
}

$foo = new Bar;
$bar = $foo;
$foobar = $bar; //SomeObject::$count = 2

---

class SomeCustomString{
protected $value;
function __unrefer($value){
if(is_string($value)){
$this->value = $value;
}
throw new UnexpectedValueException('This object can only hold strings');
}
}

$foo = new SomeCustomString;
$foo = 1;

---

Although I can't think of many uses to __refer I however can think of
one very useful use case for __unrefer - custom "types". I actually
did borrow the __unrefer functionality from SPL_Types PECL package
when trying to solve problem of how to validate contents of object
properties which are going to be set by other party and cant be
validated via set or get. I know there are ways to do this, but none
seemed pretty enough for me to actually implement.

Any feedback on this is very welcome, especially from core developers
and potential users. What would be the issues, potential drawbacks,
other?

For sure: lot of overhead on any object assignments: checking
whether __refer() exist on the variable being assigned and whether
__unrefer() exist on the destination variable.

Separate question to core developers would be, how hard it would be to
implement such functionality, or is this even possible with reasonable
effort?

Thanks, regards
Matiss Roberts Treinis <mrtreinis at gmail dot com

"Matīss Roberts Treinis" mrtreinis@gmail.com wrote:

Proposal:

Two additional magic methods for PHP objects -

__refer(void):

Refer method is called whenever object's identifier is assigned to
variable, if such method is present.
Example:

$foo = new Bar;
$bar = $foo; //__refer invoked

This assignment is handled using PHP's copy on write mechanism for any variable. A change here has massive impact on any variable assignment, function parameter passing, ... and tons of internal places.

What we have is a hook for the objects own reference counting which is affected when an object refering to an object is used in write-context by the engine, that might easily be exteded but is rather useless. (It's trivial to create an interface or abstract base class providing this addref/delref info)

Unless you can provide a robust good patch without performance penalty in cases where this isn't used this will lead nowhere, and I doubt there is a way to come up with that. (rewriting the engine might be the closest approach)

johannes