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All the Perl that's Practical to Extract and Report

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The Original Trait Researchers on the "Class Wins" Issue 12 Comments More | Login | Reply /

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  • Yes, it is really important that a programmer can see clearly when a trait method is being overridden - just as it is important that it is clear when an inherited method is being overridden.

    I agree with Dr. Black on this point, but this is just language theory and not implementation details. It can be argued that reading the source provides this feature. Dr. Black goes on to say ...

    Similarly, I agree that if the normal Perl environment does not provide good programming tools, then the implementation of traits for Perl ought to have done something to make it clear that a class method was overriding a trait method.

    Perl::Critic is a tool in the modern Perl environment that provides this, so therefore we don't have to resort to something more drastic. You however seem to reject that in this statement ...

    I suspect (though I can't prove) that many Moose developers aren't using Perl::Critic and thus aren't likely to benefit from this, thus, I agree with the traits researchers that the safety features should be in the language (or library) level rather than pushed into external tools.

    Your conclusion (obviously) leans toward your desires, but I could just have easily had said "if they are not using Perl::Critic, they should be". If people are not willing to use the tools provided them (for free) then why should the core Moose team go out of their way to do still more work simply because someone chooses not to use another perfectly good tool?

    In the end, and I have said this before, I think you are overusing roles.

    While roles are an excellent replacement for multiple inheritance they possess many of the same (or similar) dead ends and pitfalls if used too heavily. It is my opinion is that using the alias/excludes feature is a code smell and that more than 3 roles being composed into a single class is a mild code smell that if not watched careful will turn into a full blown stink.

    These are my opinions in the end so you can take them or leave them, but they are founded on many years of using roles in several big work projects, many CPAN modules and countless discussions had with others on IRC. I have probed the theory, but I have lived the practice.

    I don't know that this will necessarily cause movement on anyone's part, but it's nice to know I wasn't totally insane in my reasoning

    I think at this point, the movement needs to be yours.

    You will note here [cpan.org] that any new features for Moose must first be vetted through a MooseX module. At this point (thanks for rafl and others in the Moose team) role composition is now very hookable and you should find it much easier to create a MooseX module to so this now.

    - Stevan

    • It is my opinion is that using the alias/excludes feature is a code smell and that more than 3 roles being composed into a single class is a mild code smell that if not watched careful will turn into a full blown stink.

      We have no aliases in any of our role compositions and excludes are used very rarely. I also agree that they're a code smell. As for more than 3 roles, most of our classes use 4 or fewer roles. And we still do use inheritance. Though I tend to think that inheritance is dangerous, I've not gone so far as to completely excise it (except in a spike which was very successful).

      One might think we're overusing roles, but so far, it's worked out extremely well with very few downsides, though I readily admit tha

      • It seems to me that it would be useful for Perl(5|6) to make method overriding explicit as Java has done. Similarly, I'd like to see it made explicit when you're overriding a role method with a method defined in a class. As a compile-time error.

        So I think it'd be useful for you, Ovid, to implement a MooseX module that does this a al Stevan's suggestion. Then there'd be a feature that you could point people to using.

        Stevan, FWIW, in Smalltalk the browser isn't just a tool, it's effectively part of the langua

        • As a compile-time error.

          ... as an optional compile-time error or warning or whatever.

          Warnings and errors are affordances. A default error or warning on this behavior pessimizes legitimate, intended, and explicitly designed uses of the feature.

        • I do have MooseX::Role::Strict [cpan.org] on the CPAN. It's already uncovered several issues here at work (we had managed to work most of them out the hard way before we switched over to this). Maybe I should add MooseX::Role::Warnings to that distribution?

        • Who's going to start championing the patch to P5P that we need this feature in the Language?

          One of Moose's driving goals (which we do lose site of occasionally) is that it is Perlish. This feature (right or wrong) is not how Perl currently interprets overriding inherited methods. There are several places where Moose tries to be more strict about things than default Perl (strict/warnings enabled by default for example, though 5.11 enables strict as part of "use 5.11") and several places where things that Ste

          • Who's going to start championing the patch to P5P that we need this feature in the Language?

            I'm not sure it's possible with the language as currently implemented, unless for every method dispatch you walk the C3 ordering of ancestors looking for homophonic functions and accept that AUTOLOAD will provide a lot of ambiguity or expect everyone to override UNIVERSAL::can correctly.

      • One might think we're overusing roles, but so far, it's worked out extremely well with very few downsides

        Well this is good to hear, perhaps all your examples of edge cases and oddities have skewed my perception of your code base. Although, your anti-inheritance stance does make me think perhaps you've gotten a little too drunk on the role kool-aid.

        I guess my worry is that your not using all the tools at your disposal and therefore wanting to shape the tools you are using in such ways as to compensate

    • Oh, and as for "Here we go again", I'm not asking for or expecting any changes to Moose in this regard. I only raise this issue because there seemed to be some confusion on the part of some (perhaps myself) about why the behavior is the way that it is.

      • Yeah sorry, that was an bad title written off the cuff and then not really considered, I didn't mean it as snarky as it sounds :)
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