#25122 [Opn]: Control over typecasting objects to strings

ID: 25122 User updated by: a at b dot c dot de Reported By: a at b dot c dot de Status: Open Bug Type: Feature/Change Request Operating System: Any PHP Version: 5.0.0b1 (beta1) New Comment: Is this still open? One method that (from this angle) appears quite elegant would be to give stdClass a __toString() method that simply returns "Object" (or even "Object" and an ID#, a la resources). Then any other __toString() methods in any other classes would simply be overriding this one. The clear advantage this gives is that __toString() can be then called with impunity on any object, safe in the knowledge that it exists. The type casting engine already knows how to cast objects to arrays; if it needs to cast the object to anything else it can hapily call __toString() and proceed from there. The obvious issue hinted at in the previous paragraph is that the entity that the object is cast to may require further casting in order to fit in with whatever expression is being evaluated at the time. This is something that may happen anyway: without rigorously type-checking (at runtime) the value returned by __toString() to ensure that it really is a string, it has to be assumed that the method could return anything, ranging from Void to Null to Object. And it's all too reasonable to expect that method writers will want to return, say, integers in the expectation that they will be cast to strings as per normal. So after an object has been cast into the result of its __toString() method, that result would need to be checked again, and, if necessary, recast again. And it's the method writer's own silly fault if PHP hangs when they write something that boils down to "function __toString(){return $this;}". Previous Comments: ------------------------------------------------------------------------ [2004-04-07 03:10:41] derick@php.net It's still an open feature request Adam. ------------------------------------------------------------------------ [2004-04-06 21:42:16] amt@php.net This was changed to prevent crashes. This will hopefully be fixed in 5.1, but cannot be fixed in time for 5.0. Sorry. ------------------------------------------------------------------------ [2004-04-06 19:36:37] bendik at infofab dot no From the latest change log - 18-Mar-2004 "Changed __toString() to be called automatically only with print and echo statements. (Andi)" I can not for the life of me figure out why this has been done. Why should an object behave differently when it is echoed alone and when it is concatinated? Example: (the class "Foo" has a __toString() method defined.(returns "World")) $obj = new Foo(); echo $obj; // Produces: World! echo "Hello, " . $obj; // Produces: Hello, Object id #1 Why, oh why? ------------------------------------------------------------------------ [2003-08-17 22:17:03] a at b dot c dot de Description: ------------ String casting for objects. When used in a string context (a simple example being "echo $object;") objects are currently cast to the string "object", which is generally less than helpful. The enhancement is to allow objects to have a method called, say, "__string" or something similar that is called on an object whenever it is used in a situation where a string is expected and returns a string (or something, like a number, that can be readily cast to a string). One could, for example, have a complex number class, with properties $r and $i, with a method like function __string() { $s = $this->r; if($this->i>=0) $s.='+'; $s.=$this->i; $s.='i'; return $s; } so that one can echo or concatenate complex numbers with impunity. Many classes already possess "toString()" methods, no doubt in part to Java's influence. These generally perform the role that I am advocating for __string(), with the difference being that the latter is implicitly called whenever necessary. Calling the new method "toString()" could be hazardous for existing scripts that already use classes with methods with this name. Backward compatibility can of course be achieved by writing one of function __string() { return $this->toString(); } function toString() { return $this->__string(); } which will give the two methods identical behaviour, except of course for the fact that toString() is an ordinary method that needs to be called explicitly. Not to be confused with the operation of serialize(); __string() is intended for e.g., human-readable string representations of an object and isn't necessarily reversible to produce the original object. A complex hierarchical object might, for example, generate XML as a result of calling its __string() method; in the example above, a complex number might have a string string representation of "-12+2.5i"; something containing binary data (e.g., an image) might return a textual description of the data's contents rather than the data itself. Needless to say, if the __string() method is absent, casting reverts to the existing "cast to 'object'" behaviour. ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=25122&edit=1