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104
votes
14answers
29k views

Where does this concept of “favor composition over inheritance” come from?

In the last few months, the mantra "favor composition over inheritance" seems to have sprung up out of nowhere and become almost some sort of meme within the programming community. And every time I ...
53
votes
4answers
30k views

Why should I prefer composition over inheritance?

I always read that composition is to be preferred over inheritance. A blog post on unlike minds, for example, advocates using composition over inheritance, but I can't see how polymorphism is ...
46
votes
9answers
7k views

Code Smell: Inheritance Abuse [duplicate]

It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of ...
36
votes
5answers
2k views

How is defining that a method can be overridden a stronger commitment than defining that a method can be called?

From : http://www.artima.com/lejava/articles/designprinciples4.html Erich Gamma: I still think it's true even after ten years. Inheritance is a cool way to change behavior. But we know that it's ...
31
votes
2answers
1k views

What is the meaning of “doesn't compose”?

I see a lot of texts, especially functional programming texts, claim that certain CS concepts "don't compose". Examples are: locks don't compose, monads don't compose. I've been having a hard time ...
12
votes
9answers
2k views

Should a developer know the inner workings of the computers' hardware? [closed]

I'm not talking just how memory is assigned and memory management (things that you can learn from C for example) but rather the hardware aspect and how each component of the computer hardware works ...
12
votes
2answers
3k views

When Rob Pike says “Go is about composition”, what exactly does he mean? [closed]

From Less is Exponentially More If C++ and Java are about type hierarchies and the taxonomy of types, Go is about composition.
10
votes
5answers
543 views

Should I prefer composition or inheritance in this scenario?

Consider an interface: interface IWaveGenerator { SoundWave GenerateWave(double frequency, double lengthInSeconds); } This interface is implemented by a number of classes which generate waves ...
9
votes
5answers
1k views

How do we know to favour composition over generalisation is always the right choice?

Whether an object physically exists or not, we can choose to model it in different ways. We could arbitarily use generalisation or composition in many cases. However, the GoF principle of "favour ...
9
votes
4answers
682 views

Reducing boilerplate in class that implements interfaces through composition

I have a class: A that is a composite of a number of smaller classes, B, Cand D. B, C, and D implement interfaces IB, IC, and ID respectively. Since A supports all the functionality of B, C and D, A ...
8
votes
2answers
1k views

How do I avoid writing lots of pass-through functions in a wrapper?

I have a class, which wraps another class of a common base type. Because the base type interface is quite large this involves writing a lot of pass-through functions. I am looking for a way to avoid ...
7
votes
3answers
2k views

Is dependency injection by hand a better alternative to composition and polymorphism?

First, I'm an entry level programmer; In fact, I'm finishing an A.S. degree with a final capstone project over the summer. In my new job, when there isn't some project for me to do (they're waiting ...
6
votes
6answers
1k views

What is the actual reason that locks (sentinels) in OO are hard to reason about? [closed]

In this talk, Rich Hickey introduces Clojure. He gives an Ants demo and talks about his motivations for implementing a Software Transactional Memory (STM) system. His reasoning for STM is that ...
6
votes
1answer
386 views

Is it fair to say that “macros don't compose”?

On this blog post aphyr (who is a brilliant programmer) states: Clojure macros come with some important restrictions. Because they’re expanded prior to evaluation, macros are invisible to ...
6
votes
3answers
1k views

Looking for a real-world example illustrating that composition can be superior to inheritance [closed]

I watched a bunch of lectures on Clojure and functional programming by Rich Hickey as well as some of the SICP lectures, and I am sold on many concepts of functional programming. I incorporated some ...
6
votes
3answers
250 views

How to design a system that allows for multiple parallel extensions of the same “component”?

As a player, I found the following problems about creating and using "extensions" (aka mods) for games: 1) Whenever the game is updated, all the mods break. 2) Most mods don't work with each ...
6
votes
1answer
101 views

How to allow for custom Rules in a Entity Component System designed game engine?

So I've been doing a lot of research into game engines, and Entity Component System (ECS) seems to be the most flexible and extendable design to use. Just to summarize, in ECS the basic idea is that ...
5
votes
3answers
393 views

Composition over inheritance but

I'm trying to teach myself software engineering and coming up against some conflicting information which is confusing me. I've been learning OOP and what abstract classes / Interfaces are and how to ...
5
votes
2answers
912 views

How to use the Decorator pattern to add little functionality to big objects?

This question regards the usage of the Decorator pattern to add little functionality to objects of large classes. Following the classic Decorator pattern, please consider the following class ...
5
votes
2answers
598 views

Is it possible to refactor inheritance to composition when virtual methods are called inside the base class?

Let's say I have a class called Country and two subclasses called AI and Player. The Country class has a number of virtual methods to allow player-specific or AI-specific behavior. I want to make it ...
5
votes
1answer
504 views

Architectural Composition Languages

Recently stumbled upon this paper (PDF) talking about ACLs, or Architectural Composition Languages. They're a fusion of two earlier lines of research: Architectural Definition Languages (such as UML) ...
4
votes
6answers
1k views

What are the alternatives to “overriding a method” when using composition instead of inheritance?

If we should favor composition over inheritance, the data part of it is clear, at least for me. What I don't have a clear solution to is how overwriting methods, or simply implementing them if they ...
4
votes
2answers
1k views

How to replace inheritance with composition in this case?

I've recently read several articles about the advantages of the composition over inheritance. Their authors said that you can always replace inheritance with composition (to be precise, they say they ...
4
votes
2answers
313 views

If an entity is composed, is it still a god object?

I am working on a system to configure hardware. Unfortunately, there is tons of variety in the hardware, which means there's a wide variety of capabilities and configurations depending on what ...
4
votes
2answers
269 views

Is excessive indirection and/or redundant encapsulation a recognized concept? [closed]

I'm curious if there's a series of tendencies or anti-patterns when programming whereby a developer will always locally re-wrap external dependencies when consuming them. A slightly less vague ...
4
votes
1answer
705 views

Composition vs. Inheritance [duplicate]

Here's what is given: public interface Request {} // there are 20 subclasses of Request public class CreateUserRequest implements Request { @NotEmpty public String userName; } // request ...
4
votes
2answers
98 views

Applying composition over inheritance to Vehicle classes

I have a car maintenance garage program that has an abstract Vehicle class that has several derived classes like Car MotorCycle, etc. Each of those derived vehicles in turn is either a fuel or an ...
4
votes
2answers
2k views

OOP - Composition, Components and Composites Example?

I've been reading a bit about OOP in relation to Composition, Components and Composites. I believe I understand the fundamental principle (not sure). Can someone please provide a code example of a ...
4
votes
1answer
1k views

Inheritance, Composition and Protocols

I'm reading a book on general object oriented concepts to try and gain a solid understanding of everything. One thing that is throwing me off is the difference between Inheritance and Composition. I ...
4
votes
1answer
655 views

Inheritance in test classes

I have an interface Serializer with methods serialize and isSerializerFor. I created a first implementation of this using TDD, and ended up with a nice clean test case fully covering a nice clean ...
4
votes
1answer
715 views

Model independency in MVC and most efficient way to do method calls

TLDR: Are models supposed to be application-dependant and totally worthless when starting a new application, or are you supposed to design models independently so that they act as stand-alone ...
4
votes
1answer
660 views

How to maintain encapsulation with composition in C++?

I am designing a class Master that is composed from multiple other classes, A, Base, C and D. These four classes have absolutely no use outside of Master and are meant to split up its functionality ...
3
votes
7answers
2k views

Inheritance using non-abstract base class

This post is based on the question http://stackoverflow.com/questions/49002/prefer-composition-over-inheritance/11758048#comment15634305_11758048. Some people said - check whether there is “is-a” ...
3
votes
6answers
312 views

Can we say “If a parent class never appears in my codes except in its child class, it should be composition instead of inheritance”?

I read some posts about "composition over inheritance","where to use composition/inheritance" , "Is-a relationship..." or "Liskov substitution principle" for some time, but I am not sure if I get the ...
3
votes
2answers
4k views

Why is inheritance generally viewed as a bad thing by OOP proponents [duplicate]

I keep hearing the phrase "Favour Composition over Inheritance" from GoF which is being annoyingly mentioned repeatedly by my friend who thinks it is a valid blanket statement but is it not more ...
3
votes
5answers
193 views

What is the correct OOP relation between complex and real numbers?

On one hand class complex { double real; double imaginary; } it is composition on the other hand class complex : double { double imaginary; } it is inheritance Which one is ...
3
votes
1answer
112 views

Do conditional delegation or different member types break the Composite pattern?

Here's how I understand the composite pattern: In the composite pattern, a root object is composed of objects which may be further composed. Moreover, to be considered composite, all those objects ...
3
votes
3answers
3k views

what does composition example vs aggregation

Composition and aggregation both are confusion to me. Does my code sample below indicate composition or aggregation? class A { public static function getData($id) { //something } ...
3
votes
1answer
284 views

Does Having DI Happen in the Composition Root go against the whole point of Dependency Injection?

I am using Dependency Injection for a .NET MVC web application in which I have three basic layers: 1) Web App 2) Service Layer 3) Data Layer I inject the data layer into the service layer and the ...
3
votes
3answers
1k views

Why should one subclass instead of composite when using the Factory Method design pattern?

I'm currently learning about design patterns. I learned about the Factory Method pattern. This pattern means that in order to implement a factory to create objects, one should subclass the class that ...
3
votes
1answer
167 views

Compose nested EventEmitters elegantly

I am developing a server-side JavaScript tool, and trying to do so in a modular way. I have a Parser class that is an EventEmitter - you call parse and it will eventually emit data and end events. It ...
3
votes
4answers
598 views

Understanding UML composition better

The difference between Composition and Aggregation in UML (and sometimes in programming too) is that with Composition, the lifetime of the objects composing the composite (e.g. an engine and a ...
3
votes
1answer
297 views

Is this Hybrid of Interface / Composition kosher?

I'm working on a project in which I'm considering using a hybrid of interfaces and composition as a single thing. What I mean by this is having a contain*ee* class be used as a front for ...
2
votes
4answers
441 views

“Imprinting” as a language feature?

Idea I had this idea for a language feature that I think would be useful, does anyone know of a language that implements something like this? The idea is that besides inheritance a class can also ...
2
votes
1answer
64 views

Term for the opposite of the functional Compose operator

In functional programming, given a function f and a function g we can define a function . (compose): let (.) f g = fun x -> g (f x) Is there a term for the function which applies arguments in the ...
2
votes
5answers
2k views

How do inheritance and composition differ?

I'm wondering about the differences between inheritance and composition examined with concrete code relevant arguments. In particular my example was: Inheritance: class Do: def do(self): ...
2
votes
1answer
93 views

How minor of a case is a class appropriate for?

I'm trying to use composition in an Entity class of mine. So far, an Entity "is" Displayable(inherited an ABC), and "has" a Position(contains a point-like class). I know I will want my Entity to ...
2
votes
1answer
121 views

Are nested private classes considered composition?

Background I am considering a design that includes a public API class containing many nested private classes. I am doing this for the following reasons: Why private nesting? They will have no use ...
2
votes
2answers
148 views

Acceptable design to use public member objects in composition?

Say I have a large class called Root, which has a lot of members & functions: class Root { public: void func1(); // operates on a and b void func2(); ... private: A a; ...
2
votes
2answers
540 views

Design pattern for composition workflows

Please bear with me as I find this tricky to articulate exactly what I am after (probably not a good sign..). I have several services set up which can be combined in a particular order to create ...