Req #61147 [Sus]: No conflict resolution for properties in traits

Edit report at https://bugs.php.net/bug.php?id=61147&edit=1 ID: 61147 Updated by: gron@php.net Reported by: greywire at gmail dot com Summary: No conflict resolution for properties in traits Status: Suspended Type: Feature/Change Request Package: Class/Object related Operating System: MacOS X 10.7 PHP Version: 5.4.0RC8 Block user comment: N Private report: N New Comment: When I write 'alias', I refer to the 'as' keyword. https://wiki.php.net/rfc/horizontalreuse#conflict_resolution Verbosely, the example in the RFC (use A, B {B::bigTalk as talk;}) can be read as: use the method body of B::bigTalk and refer to it as 'talk' in the composed class. Important is here, that bigTalk ends up still in the class and has not been changed in any way by the addition of a new alias. (In the RFC's example there is even a conflict that needs resolution.) Classes just have hash-tables of methods, i.e., the method name is mapped to the method body. Method bodies are not changed at all by the traits implementation, and all references to methods are basically by name, i.e., a string. Thus, a method call will look up the method body in the hash table based on a name/string. The same is true for properties. I do not see how your idea with __get/__set works. It is still the same name of the property that would be used. And it is not clear to me how they could be distinguished. Something like that would require name-mangling like for private properties, in the trait's method. But then again, you have quite a number of possible semantics of how to handle properties. Sometimes, they are supposed to access the same, sometimes they are supposed to be distinct. That would require quite a bit of syntax/complexity. And, as I said, the academic literature on that topic brings way to much complexity for my taste. There was a proposal on the list or on the wiki to introduce a 'local' keyword. We might want to consider that for a future version. The current solution, fail if it smells like something funny is going on, seems at least to me as a compromise that avoids nasty surprises when maintaining code, and allows us to weaken the restrictions later on. Best regards Stefan Previous Comments: ------------------------------------------------------------------------ [2012-02-21 15:24:48] greywire at gmail dot com I'm trying to understand here. When you say alias, do you mean generically like "reference" or "pointer" to a method? Or is there some aliasing construct I'm not aware of in the language? Traits are supposed to be flattened in the class, so its more like a language assisted cut and paste, correct? Which means two conflicting method names have to be renamed uniquely (or not named at all?) and then a reference/alias/pointer to the desired one is put in place with the original name. I don't know how the traits are actually implemented internally... Attempting to do this by hand I see that you could, using runkit, remove the two conflicting methods and put in one "aliased" method pointing to one that was removed. But doing this with a property as you said results in a new property that does not affect the other two. I thought maybe you could set that new property with a "&$obj->renamedprop" but that doesnt work. Running through my options (thinking about if runkit could be used to fix it. I've used runkit before to sorta implement my own traits functionality) I see its a tricky problem to solve indeed. The only thing I came up with is that if at runtime PHP just removed the conflicting properties altogether so the code compiles and runs, and then the two properties (and the needed alias) could just be caught with __get/__set and handled by the user. You'd get no warning or error about the conflict, but, you would immediately know about it when you accessed one of the properties. This may seem like a hack but at least it would give people an option... Is that a palatable compromise that wouldn't be hard to implement? :) ------------------------------------------------------------------------ [2012-02-21 09:26:36] gron@php.net Unfortunately, the solution is not easy at all. One reason is the dynamic nature of PHP. You can easily access properties based on their string name: $foo = 'bar'; $this->$foo = 'foobar'; For exactly the same reason, we do NOT provide 'renaming'. The conflict resolution for methods allows to introduce an alias. Nothing more. An alias is a new name pointing to an unchanged method-body. (If you think about what that means, note that it breaks recursion in typical cases.) Thus, your proposal does not work with the current semantics. It would only result in a new property in the class that is never actually used. So far, we refrained from adding any of the constructs proposed in literature, since they would add considerable complexity. From time to time there have been proposals for related features that could make it into a future version of PHP, but for the moment being, I do not see how we can make this work without changing the nature of PHP. Suggestions are welcome of course. Thanks Stefan ------------------------------------------------------------------------ [2012-02-20 18:59:00] greywire at gmail dot com Description: ------------ There is no way to resolve a conflict in two used traits with the same property. The resolution method used to resolve conflicting method names should be able to be used similarly on properties. I realize this may be the intended behavior to discourage use of properties in traits as properties were not originally intended in traits, but since properties are allowed, there should be a way to resolve the conflict, and the solution is simple and fits with existing syntax. Test script: --------------- <?php trait testone { public $test; } trait testtwo { public $test; } //** this should work but doesn't class traittest { use testtwo, testone { testone::$test insteadof testtwo; testtwo::$test as $testalso; } } ?> Expected result: ---------------- No errors or warnings. Actual result: -------------- Parse error: syntax error, unexpected '$test' (T_VARIABLE), expecting identifier (T_STRING) in index.php on line 14 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=61147&edit=1