4 ms·

Then you're going to be pleasantly surprised, because composition is actually a genuine OOP technique and Sandi Metz advocates for exactly this kind of sane OOP

Then you're going to be pleasantly surprised, because composition is actually a genuine OOP technique and Sandi Metz advocates for exactly this kind of sane OOP focused on encapsulation and objects making sense, instead of masturbating with class hierarchies.

gigatexal 2y ago
I used to work at a flask shop that did views with 3-5 or more inherited classes. Nobody could really follow how everything worked. It was insane. Anyways yeah give me composition and flat classes all day long.
gigatexal 2y ago
What’s funny is I did composition for a take home project when interviewing at a place and they said the approach was too complicated and failed me for it. They wanted multiple inheritance instead. Fair enough. Their codebase probably had a lot of it and my not showing it probably told them I didn’t understand it.
bccdee 2y ago
But I've read the book, and her solution to the "bottles of beer" problem involves encoding all the logic into an elaborate class hierarchy! I'm not rabidly anti-OOP, but the point at which I turn against it is when the pursuit of "properly" modelling your domain with objects obscures the underlying logic. I feel like this book reaches that point. This is her stance on polymorphism: > As an OO practitioner, when you see a conditional, the hairs on your neck should stand up. Its very presence ought to offend your sensibilities. You should feel entitled to send messages to objects, and look for a way to write code that allows you to do so. The above pattern means that objects are missing, and suggests that subsequent refactorings are needed to reveal them. Absolutely not! You should not, as a rule, be replacing conditional statements with polymorphic dispatch. Polymorphism can be a useful tool for separating behaviour into modules, but that trade-off is only worthwhile when the original behaviour is too bloated to be legible as a unit. I don't see an awareness of that trade-off here. That's my problem.
- Toutouxc 2y ago
  Well, the entire book is focused on solving a laughably trivial problem, any solution is going to feel excessive. The elaborate object hierarchy that she uses would obviously feel different in real world, complicated domain. I found the excerpt in the book and I don't see her mentioning traditional class-level polymorphism (of the Java kind) anywhere around it. What SM generally advocates for is using OBJECT hierarchies to implement behaviors and encapsulate logic, the objects usually being instances of simple (and final!) free-standing classes. All thanks to the ability of any Ruby object to send messages to (call methods of) a different object, without knowing or caring about its type or origin, and the other object supplying the behavior without having to check its own type (because the correct behavior is the only one that the object, being a specialized object, even knows). This is done at runtime and is called "composition" (as in "composition over inheritance") and is different from using pre-built CLASS hierarchies to implement behaviors, aka "inheritance" (as in "composition over inheritance"). In Ruby, composition is Dog.new(Woofing.new), whereas using inheritance (class hierarchies) is Dog.new after you've done "include Woofing" inside the class. I don't know Python well, but it seems like the person in the top-level comment expressed their dislike for the second kind.
  - bccdee 2y ago
    I should clarify that the elaborate class hierarchy in the book is inheritance-based. When there's one bottle of beer on the wall, she instantiates `new BottleNumber1()`, which inherits from `BottleNumber` and overrides the method `container()` to return the singular "bottle" rather than the plural "bottles" which the base class's `BottleNumber::bottle()` would return (in the javascript edition, at least).
    - mekoka 2y ago
      Inheritance is not a banned practice. It should just be your second choice when there's a better path through composition. Do you see one here? Interfacing to address Liskov's substitution is a perfectly valid reason to "extend" in many older languages, since their inheritance and interface mechanism are conflated. The way it's done here is fine. Single parent, shallow and only for the purpose of overriding and specializing. Also, the real issue SM is trying to address is actually single responsibility and open-close, which aren't just an OO thing. As you'll design your own libraries' functional APIs, you'll have to decide whether to publish fewer functions, with a rich set of behaviors controlled through the passing of (many) parameters (and conditionals in the function body); or take a finer grain approach with multiple functions that abide as much as possible to single responsibility and only take few input about the state. I'd bet that the former will quickly raise complaints, by both maintainers and users alike, because of all the ifs and buts typically associated with it. For the same reasons, you don't want your methods to have divergent behavior based on state. You want multiple types.

gigatexal 2y ago

I used to work at a flask shop that did views with 3-5 or more inherited classes. Nobody could really follow how everything worked. It was insane. Anyways yeah give me composition and flat classes all day long.

gigatexal 2y ago

What’s funny is I did composition for a take home project when interviewing at a place and they said the approach was too complicated and failed me for it. They wanted multiple inheritance instead. Fair enough. Their codebase probably had a lot of it and my not showing it probably told them I didn’t understand it.

bccdee 2y ago

But I've read the book, and her solution to the "bottles of beer" problem involves encoding all the logic into an elaborate class hierarchy! I'm not rabidly anti-OOP, but the point at which I turn against it is when the pursuit of "properly" modelling your domain with objects obscures the underlying logic. I feel like this book reaches that point. This is her stance on polymorphism: > As an OO practitioner, when you see a conditional, the hairs on your neck should stand up. Its very presence ought to offend your sensibilities. You should feel entitled to send messages to objects, and look for a way to write code that allows you to do so. The above pattern means that objects are missing, and suggests that subsequent refactorings are needed to reveal them. Absolutely not! You should not, as a rule, be replacing conditional statements with polymorphic dispatch. Polymorphism can be a useful tool for separating behaviour into modules, but that trade-off is only worthwhile when the original behaviour is too bloated to be legible as a unit. I don't see an awareness of that trade-off here. That's my problem.

Toutouxc 2y ago
Well, the entire book is focused on solving a laughably trivial problem, any solution is going to feel excessive. The elaborate object hierarchy that she uses would obviously feel different in real world, complicated domain. I found the excerpt in the book and I don't see her mentioning traditional class-level polymorphism (of the Java kind) anywhere around it. What SM generally advocates for is using OBJECT hierarchies to implement behaviors and encapsulate logic, the objects usually being instances of simple (and final!) free-standing classes. All thanks to the ability of any Ruby object to send messages to (call methods of) a different object, without knowing or caring about its type or origin, and the other object supplying the behavior without having to check its own type (because the correct behavior is the only one that the object, being a specialized object, even knows). This is done at runtime and is called "composition" (as in "composition over inheritance") and is different from using pre-built CLASS hierarchies to implement behaviors, aka "inheritance" (as in "composition over inheritance"). In Ruby, composition is Dog.new(Woofing.new), whereas using inheritance (class hierarchies) is Dog.new after you've done "include Woofing" inside the class. I don't know Python well, but it seems like the person in the top-level comment expressed their dislike for the second kind.
- bccdee 2y ago
  I should clarify that the elaborate class hierarchy in the book is inheritance-based. When there's one bottle of beer on the wall, she instantiates `new BottleNumber1()`, which inherits from `BottleNumber` and overrides the method `container()` to return the singular "bottle" rather than the plural "bottles" which the base class's `BottleNumber::bottle()` would return (in the javascript edition, at least).
  - mekoka 2y ago
    Inheritance is not a banned practice. It should just be your second choice when there's a better path through composition. Do you see one here? Interfacing to address Liskov's substitution is a perfectly valid reason to "extend" in many older languages, since their inheritance and interface mechanism are conflated. The way it's done here is fine. Single parent, shallow and only for the purpose of overriding and specializing. Also, the real issue SM is trying to address is actually single responsibility and open-close, which aren't just an OO thing. As you'll design your own libraries' functional APIs, you'll have to decide whether to publish fewer functions, with a rich set of behaviors controlled through the passing of (many) parameters (and conditionals in the function body); or take a finer grain approach with multiple functions that abide as much as possible to single responsibility and only take few input about the state. I'd bet that the former will quickly raise complaints, by both maintainers and users alike, because of all the ifs and buts typically associated with it. For the same reasons, you don't want your methods to have divergent behavior based on state. You want multiple types.