While classes can often be used before they are "defined" (in terms of where they are located in a file), this does not apply once you introduce traits. With traits, classes must be defined before they are used. Which is a good thing to do regardless.

trait wtf {}
class A {
  use wtf;
}
class B extends A {}

Ok. I understand that classes should be defined before they are used. However there still may be a documentation bug and/or a missing warning.

I found in the doc at http://php.net/manual/en/language.oop5.inheritance.php that "Unless autoloading is used, then classes must be defined before they are used. If a class extends another, then the parent class must be declared before the child class structure. This rule applies to classes that inherit other classes and interfaces."

This doesn't seem to be strictly true. According to the doc, my working code shouldn't work! And the fact that traits change the strictness with which PHP parses classes doesn't seem to be explained anywhere, or at least I couldn't find it in the docs.

Moreover, shouldn't there be a warning when classes are used before they are defined?

I would happily send a doc patch and/or a failing test for that (potentially) missing warning, if you'd tell me that it is legit and guide me just a little bit as to where it should go (in the doc and/or test suite).

Thanks.