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All the Perl that's Practical to Extract and Report

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Rant Mode: Part III 6 Comments More | Login | Reply /

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  • What's really broken is that people think you need to inherit everything. In your example, it looks like you have a cart that should have things, not inherit things. I know this lame example shows up in a lot of Java books, but it's the wrong use for inheritance. They usually pull this stuff out to explain decorators, too, which is a pattern that is almost never needed for the example given.

    There's no reason that any of those things should have an Is-A relationship. You need a cart that contains other distinct objects, each of which share a common interface (although not necessarily a common implementation). It's that polymorphism stuff.

    I often wish that people never found out about inheritance, but they usually find out about it soon and it becomes the hammer to pound in every screw they encounter.

    • There's no reason that any of those things should have an Is-A relationship. You need a cart that contains other distinct objects,

      That's not exactly true in .NET. The Cart whould returns a strongly type collection of CartItems, not a mishmash of Object that then have to be inspect just to see what they are. And I don't understand that statement about no reason for IS-A. A CartItem IS a part...period. 100% percent of the time. You can't buy anything that's not a part...but I digress... Well sure, you coul

      • That's not exactly true in .NET. The Cart whould returns a strongly type collection of CartItems, not a mishmash of Object that then have to be inspect just to see what they are.

        It would make more sense to return a collection of objects that share similar interfaces, where these interfaces define the actions that you want to do with these objects.

        Your cart could return a collection of objects that can be IOrderable, IShippable, etc, where these are characteristics of these objects.

        • Right. I don't disagree with that statement as a solution.

          Again, by using interfaces, each different type of object has to reimplement the same code the implement the interface. That's a waste of effort when inherts takes care of that problem. To avoid duplicating code for all different types of objects implementing IPart, they'de all have to use another class..which even more effort for no good reason.

          We're not talking about unrelated objects in a collection ACTING like a part (via a common Interface), we'
      • Inheritance is only one way to look at that. An orderable item can be an object that contains a part along with an order description, coupon, etc. Those HAS-A relations, along with appropriate dispatching, don't need inheritance.

        Like I said, inheritance is beat into people's heads, so they think in terms of it when in reality the world doesn't operate that way.

    • Thanks for saying that. I wanted to pipe up but couldn’t muster the energy to be coherent.

      Inheritance is overrated. Polymorphism is the key; inheritance is not.

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