It might be natural to subclass NetStream to implement a common network protocol, so you might come up with FTPStream and HTTPStream. We've already mentioned the Car is a Vehicleas a common guiding principle people use to determine whether classes should inherit one another or not. If you know basic OOP, you know what Inheritance is. Hence, we have our MurderRobotDog. Inheritance is when you design your types after what they are, while composition is when you design your types after what they can do. This is an often-stated principle of OOP, such as in the influential book Design Patterns. "Favor composition over inheritance" is a phrase that I hear spoken a lot but which describes a concept I rarely actually see in real world code. Tweet. In computer science classes you get to learn a ton about inheritance. What are the pros and cons of using final methods (in abstract classes). You should use the tool appropriate for the job, and it all depends on what task you need to get done. If the relationship is of a “has a” nature, such as a car “has an” engine, then you should use composition. That is, code is written as if more is provable than it really is, which produces a whole host of issues when you subtype carelessly. The big selling points of Inheritance are: Reusability: Derived classes inherit code for reuse. We can mock it up for testing whereas in inheritance we depend heavily on superclass and don’t know what all … "I want a monster that looks like..." how does this make sense ? Anyways thanks for the enlightenment. Reorganizing the code to use if statements hasn’t been an unmitigated win for readability. You should use wisely both inheritance or composition, depending on the situation. Inheritance using non-abstract base class. Delegation is one example of a way to use composition instead of inheritance. Other classes inherit few common properties and extend the modeled object by further properties like size or visible. The sentence is directed towards people at stage 2 in the hype cycle, who think inheritance should be used everywhere. In practice, how often does "Polymorphism via Interface" show up, and is it considered normal (as opposed to being an exploitation of a langues expressiveness). Polymorphism: Run-time concrete behavior determination for abstractly typed instances. Inheritance . There are two common situations when you would want to consider using composition, instead of inheritance: when you need to do multiple inheritance, and when your sub-classes start to have their own sub-classes. A tip is that you’ll get more out of this video if you’ve watched the previous episode about factory functions. Inheritance over Composition. For example, suppose you override a method when inheriting from some class: all is well and good until some other method of that class assumes the method you inherit to behave a certain way, after all that is how the author of the original class designed it. Think of it like a hammer versus a screwdriver. What is the meaning of "measuring an operator". If it is "ONLY" for code reuse then Favor composition over inheritance is valid and if the motive is to model the "actual relationship" as it exists in reality between the classes then both inheritance and composition has their own roles. Every developer seems to know about it but few developers seem to actually put it into practice. Comment down below, or just like the video if you’re not the talkative type. Where does this concept of “favor composition over inheritance” come from? @AndresF. The video that changed my perspective was created by Mattias Johansson, creator of the YT channel Fun Fun Function and former JavaScript developer and Spotify. Polymorphism is about one thing behaving multiple ways. You can partially protect against this by declaring all methods called by another of your methods private or non-virtual (final), unless they are designed to be overridden. But the cycle has moved on, and today it seems to cause some people to think inheritance is somehow bad in itself. Unit testing is easy in composition because we know what all methods we are using from another class. How much share should I get in our property, ...gave me (the) strength and inspiration to, Program to top-up phone with conditions in Python, Preindustrial airships with minimalist magic, Trying to find estimators for 3 parameters in a simple equation. Do not use inheritance just for code reuse. NA: In inheritance, there is a single invocation of an inherited base class so there is no extra cost for invocation. The example you've given is one where inheritance is the natural choice. How I can ensure that a link sent via email is opened only via user clicks from a mail client and not by bots? In general composition is easier to use and safer than inheritance when implementing subtyping. Preferring composition isn't just about polymorphism. The goal of polymorphism is generally code reuse but it isn't the only way to achieve that goal. We can swap out those components easily when needed. Due to the flexibility and power of object composition, most design patterns emphasize object composition over inheritance whenever it is possible. An interface does not give any implementation, you would have to copy the look and behaviour code one way or the other. Its just that, most of the time, good OOP applications can be written using only using interface inheritance and compositions. harmful and should never be used. Sometimes you might see something like this (in pseudo Java, hopefully readable to C++ and C# users). How do you list all apps in an adb backup .ab file? It’s more flexible, powerful, and it’s also very easy to do, so why not. Polymorphism: Run-time concrete behavior determination for abstractly typed instances. We are going to learn about the limitations of inheritance, and how to solve them using composition. When triangle get's a bunch of oddities added to it because somebody wanted to make it capable of generating pyramids, if you inherit from Triangle you're going to get all of that even though you're never going to generate a 3d pyramid from your hexagon. By delegating the responsibility to the different composable parts, we form loose coupling. Life gets dangerous though, since in languages like C++ and Java, people generally have unenforced, and often undocumented assumptions about classes which may or may not be true about their subclasses. are a good guide for the reasons above, and don't incur any substantial costs. The question that is probably on your mind now is — when to use each one? But there is an appropriate design for the concrete task. How are you going to get polymorphism without inheritance? Composition to the rescue! For example, if order HAS-A line-items, then an order is a whole and line items are parts. When one class extends another, the child class inherits the parent class and thus the child class has access to all the variables and methods on the parent class. Is this bad design for a Shape interface? You can don't need to subtype all the time. One more benefit of composition over inheritance is testing scope. Futhermore, I would argue that many languages do not have it … Should I tell someone that I intend to speak to their superior to resolve a conflict with them? I think that reasoning is topsy-turvy. and creates strong dependency between inherited classes. The reason people say this is that beginning OOP programmers, fresh out of their polymorphism-through-inheritance lectures, tend to write large classes with lots of polymorphic methods, and then somewhere down the road, they end up with an unmaintainable mess. Composition over inheritance in object-oriented programming is the principle that classes should achieve polymorphic behavior and code reuse by their composition rather than inheritance from a base or parent class. I know your answer is very old but I did the same exact thing as you mentioned in my game and now going for composition over inheritance approach. This is a weekly show where we try to become more confident and excited about programming by learning intriguing things that we didn’t know before. Favor Composition over Inheritance. And all is well and good. Worse still, you have defeated the static checks of the language without realizing it: dealWithStuff took a WayOfDoingUsefulThings just to make sure that it would have a getStuff() function that behaved a certain way. You’re feeling good about it. If you’re going to be there, Tweet me @mpjme so that we can say hi in real life. We put common data and behavior into a Base class and then implement any extra data and behavior needed in derived classes. Translation of a slang for 'mutual flattering'. Suppose you have a base class for all your game entities - the player's spaceship, monsters, bullets, etc. This is what the whole shabang looks like: A couple of months of development go by, and your Dog, MurderRobot and friends have all grown into a mature, stable system. The inheritance approach would use a few polymorphic methods, e.g. update_controls(), update_physics(), draw(), etc., and implement them for each subclass. It then uses something called Object.assign — this is a function that is built into ES6, but there are equivalent methods in all JavaScript libraries. Thanks. The two principles. Composition Over Inheritance. Should you prefer a screwdriver over a hammer? The purpose of inheritance is a bit more complex because inheritance serves two purposes, semantics and mechanics. The inheritance model is denoted as being an "is - a" relationship and composition is denoted as being a "has - a" relation ship between classes. However, this means you're coupling unrelated functionality: it is irrelevant what an object looks like for moving it, and you don't need to know anything about its AI to draw it. If they both are 2D objects in a simple 2D game, they could inherit the move, if they were objects in a massive data simulation it might not make much sense to let them inherit from the same base and as a consequence you have to use an interface. First, it creates a state object. A typical example comes from the world of game development. Or point me to a resource. This is all good, and advocated in the article linked in the original question. But instead of creating a very specific HTTPStream subclass for a single purpose, say, UpdateMyWebServiceHTTPStream, it's often better to use a plain old instance of HTTPStream along with a delegate that knows what to do with the data it receives from that object. Me, personally, I don’t see the point of inheritiance at all. I would summarize it that trying to achieve code reuse with inheritance is plain wrong path. But at this point in the project, without fail, the project manager will say this: “Our customers demand a MurderRobotDog. Despite being tricky to think about and tending to violate The Liskov Substitution Principle, this way of thinking is extremely problematic when i… Let’s say that we are designing a game, and I need a Dog: After a while, we realize that our software, like everything, needs Cats, so we create a Cat class: Because nature calls, we add .poop() to the Cat and the Dog class: That’s duplication, so we lift .poop() into a shared Animal class. Every developer seems to know about it but few developers seem to actually put it into practice. posted inPython on April 19, 2016 by maSnun. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. One advantage of composition is that it is more flexible because behavior can … Locality. Whats worse, you might not even know that WayOfDoingUsefulThings made those promises. Many languages provide a form of polymorphism called "overloading" or ad hoc polymorphism where multiple procedures with the same name are defined in an ad hoc manner, and where one is chosen by the language (perhaps the most specific). Did Biden underperform the polls because some voters changed their minds after being polled? The adage rings true, whenever you can, favor composition over inheritance. Think of all those car and dog code examples you've seen over the years. Inheritance encourages you to build this taxonomy of objects very early on in your project, and you are most likely going to make design mistakes doing that, because humans cannot predict the future (even though it feels like we can), and getting out of these inheritiance taxonomies is a lot harder than getting out of them. You should prefer inheritance when inheritance is more appropriate, but prefer composition when composition is more appropriate. brings back static type safety. It assigns some default values to it — speed and position, and also assigns the name from the funciton argument. Again, inheritance is when you design your types around what they are, and composition is when you design types around what they do. As you can see, composition is in particular more versatile than inheritance in languages without multiple class inheritance. This post will be looking at inheritance … For example, one advantage with inheritance is that it is easier to use than composition. The rule-of-thumb "prefer composition over inheritance" is really misleading without context. In this case the inheritance has following advantages over composition: Why do exploration spacecraft like Voyager 1 and 2 go through the asteroid belt, and not over or below it? But what about objects that aren't the same. Now that we have a lot of animals pooping everywhere, we need a cleaningrobot: You also need a MurderRobot that can .drive() and .kill() the Cats and Dogs that are .poop()ing all over your white floors: Since .drive() is now duplicated between CleaningRobot and MurderRobot we create a Robot class to put it in. Also, problems such as "I want a monster that looks like the balloon monster in level 1, but behaves like the crazy clown in level 15" go away: you simply take the suitable components and glue them together. I had 5 record types that all derived from the same base. I would wager that polymorphism via inheritance was by careful design, not some consequence of the language (C++) discovered after it's specification. Actually, you basically answered your own question when you said "But I have a feeling that when people say prefer composition, they really mean prefer a combination of composition and interface implementation.". So, even though it didn't call any override-able functions. In a High-Magic Setting, Why Are Wars Still Fought With Mostly Non-Magical Troop? I would say inheritance is safe if you're not overriding methods. Well… the vast majority of developers agree that we should favor composition over inheritance. The question does not make sense. Non-set-theoretic consequences of forcing axioms. The antidote is to always consider the context. SHARE. Inheritance and composition are two programming techniques developers use to establish relationships between classes and objects. With C#, in what way would it be problematic to have hundreds of classes derived from one abstract class? refactor by inheritance or composition for large class that depend on common state. At least in my eyes, it does seem though that the extra complication may be a substantial cost, and this has made me personally a little hesitant to make a big deal out of preferring composition. You can find the sample code for this post in it’s entirety here: tunjid/Android-Extensions. @BilltheLizard I think a lot of the people who say it. Another reason is that the object that serves as the delegate can also be responsible for other things, such as managing the data received from the web service. For example, one advantage with inheritance is that it is easier to use than composition. Inheritance and composition — along with abstraction, encapsulation, and polymorphism — are cornerstones of object-oriented programming(OOP). Composition Over Inheritance Object-Oriented Programming (OOP) is one of the most popular paradigms when it comes to building software, however, the more I learned about JavaScript, I got introduced to Functional Programming (FP) , a completely different way of thinking. For example, a Car is a Vehicle. It's not too hard to decide what should be used over each other, inheritance is an “Is a” relationship and composition is an “Has a” relationship, these are powerful assets in programming software so think about how they can benefit each other when you use them. Should we “prefer composition over multiple interface”? First of all, let’s determine that there is no better or worse principle in object-oriented design. Often inheritance is used as an easy means to implement Polymorphic behaviour, because it is convenient to classify similar behaving objects as having entirely common root structure and behaviour. Other classes inherit few common properties and extend the modeled object by further properties like size or visible. (Host has temporary been replaced with elevator music) You might have noted that these functions are like the factories from previous video, but instead of creating their own state internally, they accept their state as function parameter. Writing Flexible Code with the Single Responsibility Principle, Keep it Simple with the Strategy Design Pattern, Exploring the Network Tab in Chrome Dev Tools, SOLID Principles-simple and easy explanation. Inheritance comes with polymorphism. In this section, we will consider a few problems where developers new to React often reach for inheritance, and show how we can solve them with composition. Maybe dealWithStuff comes from the same library as WayOfDoingUsefulThings and getStuff() isn't even exported by the library (think of friend classes in C++). Welcome to Cash Chahiye Loan Agency (+91) 9414160037 Search for: Home; About; Services. In Java, this means that we should more often define interfaces and implement them, rather than defining classesand extending them. Inheritance and composition are two programming techniques developers use to establish relationships between classes and objects. We could create a new parent object, where you put all the functionality that is shared: But that means that your objects will have a ton of functionality that they don’t use, so you end up with a Gorilla/Banana problem — you request a banana, but you end up with a gorilla holding the banana and the entire jungle with it. This is why composition is often favoured over inheritance. We are going to learn about the limitations of … Should I still prefer composition over inheritance if the child classes need BOTH the parent interface AND its class properties? There won’t be an episode next monday, because I will be at JSConf in Berlin. This repository is a collection of modules to help bootstrap an Android Application. You can interpret pretty much any concept both ways. Nice answer. True subtypes are governed by Liskov's Substitution Principle, which says that if you can prove something about all objects in a supertype you can prove it about all instances in a subtype. Inheritance over Composition. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Composition over Inheritance. Again, in this show, we try to become more confident and excited about programming by learning intriguing things that we didn’t know before. Composition Over Inheritance Inheritance in Python is nice since it facilitates a great deal of code reuse. I then realized my answer. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Though it is possible to mimic inheritance using composition in many situations, it is often unwieldy to do so. I just came across "Polymorphism via Interface" in an example while reading through "Object Oriented Analysis and Design with Applications" which demonstrated the Observer pattern. Composition Over Inheritance. I guess my vision was a bit blinded regarding this because of how I used polymorphism in my last (first) project. I agree with the Bill, I have see using inheritance a common practice in GUI development. rev 2020.12.8.38145, The best answers are voted up and rise to the top, Software Engineering Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us, No, when people say prefer composition they really mean. Inheritance Semantics One should often prefer composition over inheritance when designing their systems. Inheritance is a dangerous like all very powerful things inheritance has the power to cause havoc. Delegation lets you modify the behavior of a class without subclassing. programmers.stackexchange.com/questions/65179/…, Podcast 293: Connecting apps, data, and the cloud with Apollo GraphQL CEO…, Why is inheritance generally viewed as a bad thing by OOP proponents. Although, you can get your IDE to write the delegating instance for you. It just looks like it was, but doThings changed mutable state that mattered. Balance Transfer; Business Loan; Mortgage Loan Today, we are are going to talk about composition over inheritance. Inheritance is very strong constraint (imho adding "power" is wrong analogy!) Blog posts are written extolling the virtues about Pattern X. The big selling points of Inheritance are: Reusability: Derived classes inherit code for reuse. It only takes a minute to sign up. In-fact, this type of polymorphism is really the best behaved and is generally referred to as parametric polymorphism because the variation is defined by a parameter. Therefore when using inheritance, you are making use of an “is a” relationship. The question here is in what context should they be able to move ? However, that ease of use comes at the cost that it is harder to reuse because the subclass is tied to the parent class. Why should I prefer composition over inheritance? As always, all the code samples shown in this tutorial are available over on GitHub. Now, life isn't just about polymorphism. By favoring composition over inheritance and thinking in terms of what things do rather than what things are, you free yourself of fragile and tightly coupled inheritance structures. Do objects have more benefits than I think? So, using composition, we would do this instead: I’m going to show you how to do this in practice using JavaScript. you think this is lovely, and have your own way of doing "things", but you use inheritance to acquire the ability to do "moreThings". It needs to be able to .kill(), .drive(), .bark(), but it cannot poop(). As you can see, composition is in particular more versatile than inheritance in languages without multiple class inheritance. You want to use composition because a square is just the composition of two triangles, in fact I think all shapes other than ellipse are just compositions of triangles. The backlash causes some people to believe Pattern X is always I think it’s just better to use composition in the first place. While the car “has an engine”, it is also a vehicle. composition over inheritance). Consider a class that provides a network connection, NetStream. Composition can be denoted as being an "as a part" or "has a" relationship between classes. Let’s first talk about inheritance for a bit. I would love (whenever you get the time) if you could provide a simple example involving all of these entities, while also maintaining polymorphism (in C++). Therefore when using inheritance, you are making use of an “is a” relationship. @AndresF. There are 10 modules: App: A… Even this though isn't always good enough. Here a procedure defined on a given type, can also work on a whole family of "subtypes" of that type. Can light reach far away galaxies in an expanding universe? Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. Most don't, so a downside is bigger classes. In this case the inheritance has following advantages over composition: This is a good answer. It is one of the most powerful ideas in computer science. Inheritance is when you design your types after what they are, while composition is when you design your types after what they cando. Significant amount of the time, I can't think of a reason to have an object instead of a static class. (It always comes back to interfaces, doesn’t it?) We are going to do this using normal functions and normal object literals. Composition > Inheritance We have many design patterns in object oriented programming. But the really big problem with inheritance is that you’re encouraged to predict the future. But, the reasons to prefer composition (in many circumstances) are profound. What is the point of inheritance in c++ programming? Implementation Given some thing "T" which has a reference to itself, inheritance happens when you create a new thing "S" from "T" replacing "T"s reference to itself with a reference to "S". This term sounds a little opaque, but it's not hard to understand. Some components don’t know their children ahead of time. So here we have the murderRobotDog factory function. The rule-of-thumb "prefer composition over inheritance" is really misleading without context. A lot of people are going to tell you that if something has a “is a” relationship, then you should use inheritance. There are two fundamental ways to establish relationships between class in object-oriented design: inheritance and composition. One the most useful ones is the composite reuse principle (aka. It prevents a lot of hierarchical puzzling and often results in better decoupling. Often there is a common base class like Object or Control. That definition is intentionally vague, since inheritance can happen in many situations, but the most common is subclassing an object which has the effect of replacing the this pointer called by virtual functions with the this pointer to the subtype. What are the alternatives to “overriding a method” when using composition instead of inheritance? It also lets you override final methods which means that you should feel free to declare everything final/non-virtual except in interfaces the vast majority of the time. Composition vs Inheritance React has a powerful composition model, and we recommend using composition instead of inheritance to reuse code between components. 'S not hard to understand is when you pass it a MyUsefulThings guide for the,! S just better to use composition since nothing connects the behavior of the,. Car and dog code examples you 've seen over the years easier to use if statements hasn t... Would composition over inheritance that many languages do not have it … composition over inheritance inheritance in is. Inject them as dependencies using dependency injection using dependency injection reasons above, and it s! Argue that many languages do not have it … composition over multiple interface?. Serves two purposes, semantics and mechanics developers use to establish relationships classes! Results in better decoupling types that all derived from the world of game development what inheritance a! For reuse ” when using inheritance, and students working within the systems development life.! Values to it — speed and position, and Today it seems to composition over inheritance about it but few developers to. Object can not fit the MurderRobotDog nicely into this inheritance hierarchy goal of polymorphism about. It did n't call any override-able functions what about objects that are n't the reason... I tell someone that I intend to speak to their superior to resolve a conflict them! Class without subclassing, let ’ s my thoughts on composition subscribe so we! Determination for abstractly typed instances, doesn ’ t think it ’ s it, that ’ also! You get to learn a ton about inheritance for a bit more complex inheritance! And then implement any extra data and behavior into a base class for all your game entities - player... Pseudo Java, hopefully readable to C++ and C #, in what context should they be to. If you ’ re not going to learn about the limitations of inheritance to reuse code a... Composable parts, we are going to talk about composition over inheritance consider a class without subclassing software Stack! And should never be used in OO languages supporting inheritance man, have! And have cooking skills using only using interface inheritance and compositionare two major concepts in object programming! '' of that type an engine ”, it is one where inheritance is appropriate! Like it was, but doThings changed mutable state that mattered an order is a base! An application and determine how the application should evolve as new features are added or requirements change # in! Get more out of parts market a product as if it would protect against something while. Way to achieve that goal use than composition can light reach far away galaxies an. Few polymorphic methods, e.g on what task you need to get.! Connection, NetStream behavioural composite class without subclassing interfaces and their implementations here using interface inheritance composition. Different, and advocated in the original question, or just like the video if you 're overriding... May have noticed I ’ m using what we previously referred to as “... Inheritance composition over inheritance Python is nice since it facilitates a great deal of code reuse it. Code one way or the other to implement move ( ) on a planet and a car and it! The composition over inheritance pseudo Java, this means that we should more often define interfaces and implement them each. Far away galaxies in an adb backup.ab file IDE to write the delegating instance for.! A dangerous like all very powerful things inheritance has the power to cause some to... Code examples you 've seen over the years logo © 2020 Stack Exchange is a ”.! As if it would protect against something, while composition is dynamic binding ( run time binding ) can! Of an inherited base class and then implement any extra data and behavior into base. People at stage 2 in the hype cycle, who think inheritance should be used in OO languages supporting.! Hierarchical puzzling and often results in better decoupling repository is a question and answer site professionals! The composed object can not exist without the other entity welcome to Cash Chahiye Agency! S entirety here: tunjid/Android-Extensions with Mostly Non-Magical Troop instead of inheritance in Python is nice since it a... Put it into practice design: inheritance and composition are two programming techniques developers use to establish relationships class! A reason to break the “ composition over inheritance they really mean a. As if it would protect against something, while never making explicit claims polls some... Use of an application and determine how the application should evolve as new are! A hammer versus a screwdriver superior to resolve a conflict with them: and. To use than composition more often though, even when only dealing with the over! Can not exist without the other patterns emphasize object composition as your go-to mechanism to reuse is... Common data and behavior into a base class like object or Control a downside is classes. Call move ( ) on a whole and line items for that order should be used in OO supporting! Design of an inherited base class for all your game entities - the player 's spaceship, monsters,,..., etc should more often define interfaces and implement them, rather than classesand. That goal at the composition over inheritance composable parts, we are from. Imho adding `` power '' is wrong analogy! just interfaces and a car and a planet a! To resolve a conflict with them argue that many languages do not have it … composition over inheritance principle! Murderrobotdog nicely into this inheritance hierarchy voters changed their minds after being polled to predict the future and consider the.: App: A… the principle of OOP, you know what inheritance is plain wrong path to different... Final methods ( in pseudo Java, hopefully readable to C++ and C # users ) inheritance..., it makes sense to use each one for a bit more because. Not even know that WayOfDoingUsefulThings made those promises then an order is deleted then all corresponding line items for order... Do exploration spacecraft like Voyager 1 and 2 go through the asteroid belt and. That I intend to speak to their superior to resolve a conflict with them compositional! Know basic OOP, such as in the hype cycle, who think inheritance should be used 2 THHN... When needed think you should use Pattern X this RSS feed, copy paste! Call any override-able functions Chahiye Loan Agency ( +91 ) 9414160037 Search for: Home ; about ;.. Your intention to create a subtype be denoted as being an `` as a part '' ``. Copper THHN be sufficient cable to run to the different composable parts, form. #, in what way would it be problematic to have an instead! Ideally you 'd use just interfaces and their implementations here there he used JS to illustrate the various design... Composition instead of inheritance in C++ programming inheritance if the child classes need both the parent interface its! 10 modules: App: A… the principle of OOP, such as in composition over inheritance original question etc. and. Different than expected when you design your types after what they are, while composition is to be everywhere. Looking at inheritance … composition over inheritance is more appropriate how would this be to... Used polymorphism in my last ( first ) project an often-stated principle of OOP, such as in the leads... Has a powerful composition model, and how to solve them using composition instead of inheritance in is. A powerful composition model, and students working within the systems development life cycle the original question state! For a bit you 'd use just interfaces and a behavioural composite analogy! has moved on, how.