I do like the idea of an explicit mechanism in Perl to declare that a class provides its own implementation for an interface, since as it stands now you must search @ISA for the abstract base class and then at runtime see if those methods actually permit themselves to be used. (Note that it's common to die or throw an Exception or Error inside those "abstract" methods in the case they are called directly or not overridden in subclasses.) I think this is sound theoretically -- I reiterate that inheritance of interface constitutes an is-a relationship -- however it is a pain. What I'd like is to say: 

use base Car;
use interface Drivable; # a little cleaner than chromatic's example co
+de IMHO

[download]

and have the interface pragma enforce the proscription against non-static data members and method implementations. Discovering if a class implements an interface then is the simpler task of querying the implements hash or array.

The major obstacle to acceptance of the Date & Darwen idea of inheritance is that it's not what most programmers mean when they talk about object-orientation. The definition of an "object" is the synthesis in a single entity of state and behavior. I have no objection to the judicious separation of these two things into i.e., structs or class methods, however a class with methods but no instance data does not define an object, and neither does a class with data but no methods. (Hmm, "Methods without data are empty, data without methods are blind" :^) This is why I'm saying that "implementation" covers all aspects of how a class does its business, including not just the data members, but the member functions as well. Now if all you want out of an object is its data, then subclassing is inappropriate; rather, you should simply pull what you need from the object and store it elsewhere, where you don't need to ensure that it won't be acted upon using its natural inherited behavior.

In reply to Re: Re: Re: Re: Class::Interface -- isa() Considered Harmful by djantzen
in thread Class::Interface -- isa() Considered Harmful by chromatic

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.