Add support for checking trait usage to class_uses()

[dshafik]

This patch adds support for:

<?php
if (class_uses($classnameOrObject, $autoload, $traitName)) {
    // returns boolean
}
?>

[nikic]

In my eyes it isn't good to overload a function with two completely different behaviors, namely a) returning all used traits and b) checking whether a particular one is used. Also the fact that there is an autoload parameter in between makes it kinda ugly to use. I'd prefer the separate function here, as proposed in #23. (Though I'd even more prefer no function at all ^^)

[dshafik]

@nikic this allows us to implement desired functionality, without littering the global namespace, and is far better IMO than needing to do:

<?php
if (isset(class_uses($classnameOrObject, $autoload)[$traitName])) {

}
?>

[MagicalTux]

Maybe implementing a separate method for this check would make more sense. Having one method have two separate behaviors do not sound clean.
By the way any way to see that check parent classes' traits too ?

[dshafik]

@MagicalTux If you look at the tests, you will see that it does check parent classes' traits. Also, PR #23 is a separate function, this is an alternative explicitly so that we don't need a new function.

[smarr]

Without judging the merits of this proposal, please keep consistency with related functions.

If this functionality needs to be added for traits, it is also necessary for interfaces: http://www.php.net/manual/en/function.class-implements.php

And such proposals are probably best discussed on the internals mailing list.

[php-pulls]

Comment on behalf of nikic at php.net:

Closing this for the reasons outlined in PR #23, namely that traits can not be used as interfaces and thus checking whether a particular traits was implemented doesn't make much sense.