Hi Nathan:
On 11 Dec 2010, at 19:35, Nathan Nobbe wrote:
> Regarding visibility modifiers, why not carry them over from the trait
> directly, private in the trait definition results in private in the class
> definition.
The problem will be hopefully more clear in the following example:
trait StateMachineDoor {
private $currentState;
public function open() {....}
}
trait StateMachineElevator {
public $currentState;
public function callElevator() { ... }
}
These two traits are not compatible since currentState has different semantics
in both traits.
With the current design of traits, there is no language solution to this
problem.
The suggestions to avoid the problem are to use better names like
$currentDoorState and $currentElevatorState, or to rely on accessors which is
currently the only variant in which the programmer will notice that there is an
incompatibility:
trait StateMachineDoor {
abstract function &getCurrentState();
public function open() {....}
}
trait StateMachineElevator {
abstract function &getCurrentState();
public function callElevator() { ... }
}
However, you might have a different situation, one where the traits are
composable with respect to their state, i.e., they need to work on the same
state:
trait OutputIterator {
public $array; // not sure why that is public here, but the implementor
chose to make it public...
public function printNext() {...}
}
trait SortArray {
private $array; // this developer chose to make the array private, for what
ever reason...
public function doSort() { ... }
}
I hope that makes the possible situations clear: state can either be composable
or not, that really depends
on the trait. And there is no language solution for it build in at the moment.
So, back to my original question:
class SomethingOutputableAndSortable {
use OutoutIterator, SortArray;
}
What is the visibility of $array supposed to be in this class? private or
public?
And further, in the very first example of this mail, ideally there should be
some warning, however, that warning would be annoying for the last example,
since here the state does not collide...
Best regards
Stefan
PS: there has been discussion on stateful traits before, but the language
solutions to that where considered to complex.
--
Stefan Marr
Software Languages Lab
Vrije Universiteit Brussel
Pleinlaan 2 / B-1050 Brussels / Belgium
http://soft.vub.ac.be/~smarr
Phone: +32 2 629 2974
Fax: +32 2 629 3525
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