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Date: Fri, 10 Dec 2010 09:49:46 -0700
Message-ID: <AANLkTi=qDh-F6_DSgZELaBd5jfsqEJN4yqEYusdnwY-v@mail.gmail.com>
To: Stefan Marr <php@stefan-marr.de>
Cc: internals@lists.php.net
Content-Type: multipart/alternative; boundary=001636c5a9f659370404971124df
Subject: Re: [PHP-DEV] Traits expecting interfaces implicitly leads to
 expensive runtime checks
From: quickshiftin@gmail.com (Nathan Nobbe)

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On Thu, Dec 9, 2010 at 4:04 PM, Stefan Marr <php@stefan-marr.de> wrote:

> Hi Nathan:
>
>
> On 09 Dec 2010, at 23:42, Nathan Nobbe wrote:
> > What I'm getting at is the scenario when a trait is designed to be used
> in
> > concert with the class in which it is being used.  In this case the trait
> > expects certain functions to be available on the class in which it is
> used
> > with.  If the methods aren't there (or checked for at runtime) a fatal
> error
> > is raised.
> >
> > A quick example
> > <?php
> > class A {
> >  use AHelper;
> >
> >  function blah() {}
> > }
> >
> > trait AHelper {
> >  function meh() {
> >    // hoping we get used w/ instances of A ...
> >    return $this->blah() * 5;
> >  }
> > }
> >
> > class B {
> >  use AHelper;
> >
> >  /// waiting for a runtime error if blah() is ever called ..
> > }
> > ?>
> >
> > Do you see what I mean?
> No, do not really see what you are getting at.
>
> How is your approach using the instanceof checks (from the first mail)
> different from changing AHelper to require blah() by stating this
> requirement using an abstract method definition?
> For the trait it is not important where that method is implemented, it just
> has to be in the final composed class.
>
> So, why don't you want the following trait?
>
> trait AHelper {
>  abstract function blah();
>
>  function meh() {
>   // hoping we get used w/ instances of A ...
>   return $this->blah() * 5;
>  }
>
> }
>

Ahh, I see how the abstract methods are working in traits now, I didn't
catch that from your first post; thanks for showing that to me.


> You want to avoid the fatal error during runtime, right?
>

Yes, exactly, and the runtime check for expected interface / class / method.


> Do you prefer dynamic checks over compile time checks?


Def not :D, however, I still think this paradigm is lacking.  Don't you
think it makes more sense if I write a trait that expects a given interface
or class to be able to specify said interface/class in it's entirety with
just a single identifier rather than listing out all the methods?

For example, I think this would be ugly
<?php
trait IteratorHelper{
abstract public current();
abstract public key();
abstract public next();
abstract public rewind();
abstract public valid();
}
?>

essentially you're redeclaring the entire interface in the trait, the same
would be true of the public interface of an expected class.  i think it
would be much more elegant to allow a specification on the trait declaration
itself, something like

<?php
trait IteratorHelper expects Iterator {
...
}
?>

-nathan

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