Why is immutable good

It would be possible to create mutable subclasses and thus ruining your hard work. It takes a concious effort to create immutable classes but it should be your target wherever possible. Do not do this! Create code on demand and do not optomize early. Unless you're in a crazy high performance environment and you're almost certainly not then it really isn't an issue. Objects are cheap. Even Oracle thinks so:. This is a classic case of eagerly optomising code.

There are obvious exceptions; data structures tend to be much easier to implement and more performant if using mutability. As always, apply common sense to your approach, but default to immutability. Thanks for visiting DZone today,. Mutation Tracking One of the advantages of immutability is that you can optimize your application by making use of reference and value equality.

This makes it easy to identify if anything has changed. You can consider the example of state change in the React component. Immutability allows you to track the changes that happen to these objects like a chain of events. Variables have new references that are easy to track compared to existing variables. This helps in debugging the code and building the concurrent application. Also, event debuggers help you to replay DOM events with video playbacks that work on tracking mutation.

For the first time, the concept of immutability might be confusing for you. You can do better if you understand the need and benefits of immutability. When the state is mutated you bump into many errors and dealing with it makes you much better in understanding the concept of immutability.

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Article Contributed By :. Both mutable and immutable objects have their own uses, pros and cons. That's right. Especially in GUI programming, mutable object are very handy. It's not just resistance, I'm sure lots of devs would love to try out the latest and greatest, but how often do new projects spin up in the average dev's environment where they can apply these new practices? Not everone can or will write a hobby project just to try out immutable state.

Two small caveats to this: 1 Take the moving game character. The Point class in. NET for instance is immutable but creating new points as the result of changes is easy and thus affordable. Strings are often large, and usually benefit from immutability. I once rewrote a complex graph class to be immutable, making the code simpler and more efficient. In such cases, having a mutable builder is the key. KonradRudolph, good points, thanks.

I did not mean to rule out using immutability in complex objects, but implementing such a class correctly and efficiently is far from being a trivial task, and the extra effort required may not be always justified. You make a good point about state vs identity. This is why Rich Hickey author of Clojure broke the two apart in Clojure.

They have the same identity, but they are not the same, every "tick" of our reality's time creates a clone of every object in our world, our brains then simply stitch these together with a common identity. Clojure has refs, atoms, agents, etc. And maps, vectors and lists for actual time. Show 15 more comments. In most modern IDEs I know, it takes practically the same amount of effort to generate only getters, as to generate both getters and setters.

Although it is true that adding final , const etc. That also discourages this sort of thing. That might be overcome with more communication and education, e. It is true that a good project has a common coding style which is not just an amalgam of the coding styles favoured by every past and present project member. So introducing or changing coding idioms should be a team decision. If you want only immutable objects, it is best to switch to a functional language.

You still need a way for the state of the program to change incrementally, and for this you need builders, or popsicle immutability, or mutable proxies, all of which take about 1 billion times the effort just dropping the setters took. Show 3 more comments. With complex systems this could easily lead to completely wiping and rebuilding the entire system's object graph Most developers don't make anything where the performance requirements are significant enough that they need to focus on concurrency or a lot of other issues that are universally considered good practice by the informed.

Contains immutablePerson? IndexOf newPerson! IndexOf immutablePerson! IndexOf newEvent! IndexOf immutableEvent! I actually provided a code example to explain how it was necessarily true in certain cases which happen to be very common in application development.

I don't believe that Java is the culprit. As I said, I'd be happy to evaluate any constructive alternatives you would suggest, but at this point you're comments sound a lot like "You're wrong because I said so". As usually implemented in Java it does require mutability I agreed with you on that point.

I'm not saying this approach is practical in Java; just that it's possible. For this to work, the reference would have to be stored somewhere else like a static class.

Am I understanding your intention correctly? It is possible to store a bidirectional relationship for immutable data as Chthulhu points out via laziness.

Here is one way to do this: haskell. Show 10 more comments. Paul Sanwald. Is this the Okasaki book? I guess the biggest advantage is when you actually want to keep the old version around as well. While the last sentence has probably been true in the past its not clear that it will remain true in the future, given current hardware trends etc. Add a comment. Perhaps "known" rather than "popular" would be a better choice of word. Yes, that's right.

I also use immutable objects if possible and, while mutable objects are still needed very often, it is amazing how often you can use immutable ones. I read this comment of mine after two and a half years, and my opinion has changed in favour of immutability. In my current project which is in Python we are using mutable objects very very seldom. Even our persistent data is immutable: we create new records as the result of some operations and delete old records when they are not needed any more, but we never update any record on disk.

Needless to say, this has made our concurrent, multiuser application much easier to implement and maintain up to now. Jerry Coffin. This is probably a big point For a "Hello World" program it is probably easiest. Managing object state-changes via a slew of mutable properties Excellent point. Of course this creates systems with little to no state-transition rules or a common means by which to implement them unfortunately.

I am not entirely sure after many projects now what is better for expediency, extensibility and correctness. I tend to think a hybrid. Dynamic ORM goodness but with some definitions for which fields are required and what state changes should be possible. What should happen to BobsTruck? Here is a short list of arguments: immutable objects are simpler to construct, test, and use truly immutable objects are always thread-safe they help to avoid temporal coupling their usage is side-effect free no defensive copies identity mutability problem is avoided they always have failure atomicity they are much easier to cache People are using mutable objects, as far as I understand, because they are still mixing OOP with imperative procedural programming.

There are four problems with this mostly having to do with data binding : Java Constructors reflection meta-data does not retain the argument names. Java Constructors and methods do not have named parameters also called labels thus it gets confusing with many parameters. When inheriting another immutable object proper order of constructors must be called.

This can be rather tricky to the point of just giving up and leaving one of the fields non-final. Adam Gent. Also immutable objects almost eliminate the entire class of state bugs.

Immutable state is still state. Your function can be pure even your state is mutable. You shouldn't use any limitations like immutability if you actually don't have a serious reason. If you want to "Undo" some state, you can create transactions. If you want to simplify communications you can send events with immutable data. It is up to you. I am writing this message from post marxism republic.

I am sure that radicalization of any idea is a wrong way. My other answer addresses the question from a very practical standpoint, and I still like it. I've decided to add this as another answer rather than an addendum to that one because it is a boring philosophical rant which hopefully also answers the question, but doesn't really fit with my existing answer.

Even in small projects immutability can be useful, but don't assume that because it exists it's meant for you.

NOTE: for the purpose of this answer I'm using the word 'discipline' to mean self-denial for some benefit. This is similar in form to another question: "Should I use Typescript? Why are types so important in JavaScript? It has a similar answer too. Consider the following scenario:.

Your semi-technical boss reads something about Typescript-as-the-new-hotness and suggests that we may want to move to it but leaves the decision to you. So you read about it, play with it, etc. Typescript has some compelling advantages: intellisense, catching errors early, specifying your APIs upfront, ease of fixing things when refactoring breaks them, fewer tests. Typescript also has some costs: certain very natural and correct JavaScript idioms can be tricky to model in it's not-especially-powerful type system, annotations grow the LoC, time and effort of rewriting existing codebase, extra step in the build pipeline, etc.

More fundamentally, it carves out a subset of possible correct JavaScript programs in exchange for the promise that your code is more likely to be correct. It's arbitrarily restrictive. That's the whole point: you impose some discipline that limits you hopefully from shooting yourself in the foot.

In the scenario described, I would contend that if you are very familiar with a small-to-middling JS codebase, that the choice to use Typescript is more aesthetic than practical. And that's fine , there's nothing wrong with aesthetics, they just aren't necessarily compelling.

You change jobs and are now a line-of-business programmer at Foo Corp. Even documentation wasn't that big a deal, even coming back to a particular portion of the code after 6 months you could figure it out easily enough.

But now discipline isn't just nice but necessary. That discipline may not involve Typescript, but will likely involve some form of static analysis as well as all the other forms of coding discipline documentation, style guide, build scripts, regression testing, CI. Discipline is no longer a luxury , it is a necessity. All of this applied to GOTO in your dinky little blackjack game in C could use GOTO s and spaghetti logic and it just wasn't that big a deal to choose-your-own-adventure your way through it, but as programs got bigger and more ambitious, well, undisciplined use of GOTO could not be sustained.

And all of this applies to immutability today. But as with all useful disciplines, there comes a point at which it is no longer optional. If I want to maintain a healthy weight, then discipline involving ice cream may be optional. But if I want to be a competitive athlete, my choice of whether or not to eat ice cream is subsumed by my choice of goals. If you want to change the world with software, immutability might be part of what you need to avoid it collapsing under it's own weight.

Me too :d. But this is normal with mutability in javascript. When You expect null but get some object. What is under userMessage on same line in immutable code? Can You guess by which method " id " is updated in mutable code in Snippet 1?? By sendMessageViaEmail. Why not? Well it was at first updated by saveMessage, but then overridden by sendMessageViaEmail.

In mutable code people didn't received push messages sendMessageViaMobilePush. Can You guess why?? For me it wasn't. Note that when complexity rise it is too difficult to check what was set and where especially when You work with other people. I've created a framework agnostic open source MIT lib for mutable or immutable state which can replace all those immutable storage like libs redux, vuex etc With deep-state-observer I can update only one node with dot notation and use wildcards.

With deep-state-observer I can fine-tune things and I have grain control over component behavior so performance can be drastically improved. Suppose we have an object called arr.

This object is valid when all the items are the same letter. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Why is immutability so important or needed in JavaScript?

Ask Question. Asked 5 years, 10 months ago. Active 1 month ago. Viewed 56k times. Improve this question. Jonathan Soifer 2, 5 5 gold badges 23 23 silver badges 49 49 bronze badges.

Relevant: programmers. Immutable data structure and pure function lead to referential transparency, making it a lot easier to reason about the behaviour of your program. You also get backtracking for free when using functional data structure.

I provided a Redux point of view bozzmob. It may be usefull to learn about immurability in general as a concept of functional paradigm instead of trying to think that JS has somehing to do with it. React is written by fans of functional programming. You have to know what they know to understand them. It's not necessary, but it does offer some nice trade offs. Show 1 more comment. Active Oldest Votes. Predictability Mutation hides change, which create unexpected side effects, which can cause nasty bugs.

Performance Even though adding values to an immutable Object means that a new instance needs to be created where existing values need to be copied and new values need to be added to the new Object which cost memory, immutable Objects can make use of structural sharing to reduce memory overhead.

Mutation Tracking Besides reduced memory usage, immutability allows you to optimize your application by making use of reference- and value equality. Improve this answer. My intention was to illustrate the concept and explicitly show that Objects are not being mutated and not necessarily to show how to implement it all the way.

However, my example might be a bit confusing, I'll update it in a bit. No that is not correct, you need to enforce immutability in the reducer yourself. This means you can follow strategies like demonstrated in the videos or use a library like immutablejs. You can find more info here and here.

Mathias Bynens wrote a great blog article about it. I agree it's an important distinction. Please explain this "Mutation hides change, which create unexpected side effects, which can cause nasty bugs. Show 3 more comments. Long answer: read below. Why is immutability so important or needed in javascript?