[recursive]

Immutability is also overrated. I mostly blame react for that. It has done a lot to push the idea that all state and model objects should be immutable. Immutability does have advantages in some contexts. But it's one tool. If that's your only hammer, you are missing other advantages.

[drob518]

The only benefit to mutability is efficiency. If you make immutability cheap, you almost never need mutability. When you do, it’s easy enough to expose mechanisms that bypass immutability. For instance in Clojure, all values are immutable by default. Sometimes, you really want more efficiency and Clojure provides its concept of “transients”[1] which allow for limited modification of structures where that’s helpful. But even then, Clojure enforces some discipline on the programmer and the expectation is that transient structures will be converted back to immutable (persistent) structures once the modifications are complete. In practice, there’s rarely a reason to use transients. I’ve written a lot of Clojure code for 15 years and only reached for it a couple of times.

[1] https://clojure.org/reference/transients

[iLemming]

Immutability is really valuable for most application logic, especially:

- State management

- Concurrency

- Testing

- Reasoning about code flow

Not a panacea, but calling it "overrated" usually means "I haven't felt its benefits yet" or "I'm optimizing for the wrong thing"

Also, experiencing immutability benefits in a mutable-first language can feel like 'meh'. In immutable-first languages - Clojure, Haskell, Elixir immutability feels like a superpower. In Javascript, it feels like a chore.

[DoomDestroyer]

A lot of these concepts don't mean anything to most developers I've found. A lot of the time I struggle to get the guy I work with to compile and run his code. Even something relatively simple as determinism and pure functions just isn't happening.

This is shockingly common and most developers will never ever hear of Clojure, Haskell or Elixir.

I really feel there is like two completely different developer worlds. One where these things are discussed and the one I am in where I am hoping that I don't have to make a teams call to tell a guy "please can you make sure you actually run the code before making a PR" because my superiors won't can him.

[drob518]

Well, yes, if your shop hires poorly, immutability won’t save you. In fact, nothing will save you.

[recursive]

> Not a panacea, but calling it "overrated" usually means "I haven't felt its benefits yet" or "I'm optimizing for the wrong thing"

I think immutability is good, and should be highly rated. Just not as highly rated as it is. I like immutable structures and use them frequently. However, I sometimes think the best solution is one that involves a mutable data structure, which is heresy in some circles. That's what I mean by over-rated.

Also, kind of unrelated, but "state management" is another term popularized by react. Almost all programming is state management. Early on, react had no good answer for making information available across a big component tree. So they came up with this idea called "state management" and said that react was not concerned with it. That's not a limitation of the framework see, it's just not part of the mission statement. That's "state management".

Almost every programming language has "state management" as part of its fundamental capabilities. And sometimes I think immutable structures are part of the best solution. Just not all the time.

[iLemming]

I think we're talking past each other.

> I like immutable structures and use them frequently.

Are you talking about immutable structures in Clojure(script)/Haskell/Elixir, or TS/JS? Because like I said - the difference in experience can be quite drastic. Especially in the context of state management. Mutable state is the source of many different bugs and frustration. Sometimes it feels that I don't even have to think of those in Clojure(script) - it's like the entire class of problems simply is non-existent.

[recursive]

Of the languages you listed, I've really only used TS/JS significantly. Years ago, I made a half-hearted attempt to learn Haskell, but got stuck on vocabulary early on. I don't have much energy to try again at the moment.

Anyway, regardless of the capabilities of the language, some things work better with mutable structures. Consider a histogram function. It takes a sequence of elements, and returns tuples of (element, count). I'm not aware of an immutable algorithm that can do that in O(n) like the trivial algorithm using a key-value map.

[iLemming]

> I made a half-hearted attempt to learn Haskell

Try Clojure(script) - everything that felt confusing in Haskell becomes crystal clear, I promise.

> Consider a histogram function.

You can absolutely do this efficiently with immutable structures in Clojure, something like

      (reduce (fn [acc x]
                (update acc x (fn [v] (inc (or v 0)))))
              {}
              coll)

This is O(n) and uses immutable maps. The key insight: immutability in Clojure doesn't mean inefficiency. Each `update` returns a new map, but:

1. Persistent data structures share structure under the hood - they don't copy everything

2. The algorithmic complexity is the same as mutable approaches

3. You get thread-safety and easier reasoning for a bonus

In JS/TS, you'd need a mutable object - JS makes mutability efficient, so immutability feels awkward.

But Clojure's immutable structures are designed for this shit - they're not slow copies, they're efficient data structures optimized for functional programming.

[pka]

> immutability in Clojure doesn't mean inefficiency.

You are still doing a gazillion allocations compared to:

  for (let i = 0; i < data.length; i++) { hist[data[i]]++; }

But apart from that the mutable code in many cases is just much clearer compared to something like your fold above. Sometimes it's genuinely easier to assemble a data structure "as you go" instead of from the "bottom up" as in FP.

[recursive]

Next time I feel an itch to learn a language, I'll probably pick Clojure, based mostly on this comment. Not sure when that will be though.

[no_wizard]

I just want a way of doing immutability until production and let a compiler figure out how to optimize that into potentially mutable efficient code since it can on those guarantees.

No runtime cost in production is the goal

[iLemming]

> No runtime cost in production is the goal

Clojure's persistent data structures are extremely fast and memory efficient. Yes, it's technically not a complete zero-overhead, pragmatically speaking - the overhead is extremely tiny. Performance usually is not a bottleneck - typically you're I/O bound, algorithm-bound, not immutability-bound. When it truly matters, you can always drop to mutable host language structures - Clojure is a "hosted" language, it sits atop your language stack - JVM/JS/Dart, then it all depends on the runtime - when in javaland, JVM optimizations feel like blackmagicfuckery - there's JIT, escape analysis (it proves objects don't escape and stack-allocates them), dead code elimination, etc. For like 95% of use cases using immutable-first language (in this example Clojure) for perf, is absolutely almost never a problem.

Haskell is even more faster because it's pure by default, compiler optimizes aggressively.

Elixir is a bit of a different story - it might be slower than Clojure for CPU-bound work, but only because BEAM focuses on consistent (not peak) performance.

Pragmatically, for the tasks that are CPU-bound and the requirement is "absolute zero-cost immutability" - Rust is a great choice today. However, the trade off is that development cycle is dramatically slower in Rust, that compared to Clojure. REPL-driven nature of Clojure allows you to prototype and build very fast.

From many different utilitarian points, Clojure is enormously practical language, I highly recommend getting some familiarity with it, even if it feels very niche today. I think it was Stu Halloway who said something like: "when Python was the same age of Clojure, it was also a niche language"

[drob518]

This doesn’t make much sense. One of the benefits of immutability is that once you create a data structure, it doesn’t change and you can treat it as a value (pass it around, share it between threads without cloning it, etc.). If you now allow modifications, you’re suddenly violating all those guarantees and you need to write code that defensively makes clones, so you’re right back where you started. In Clojure, you can cheat at points with transients where the programmer knows that a certain data structure is only seen by a single thread of execution, but you’re still immutable most of the time.

[no_wizard]

Depends on your target. Clojure targets the JVM by default and that has very different constraints than say, compiling to JavaScript for the browser or node.

Compiling to a JS engine this would be great because immutability has a runtime cost

[iLemming]

Clojurescript supports transients https://clojureverse.org/t/transients-in-clojurescript/9102/...

Runtime cost of using Clojurescipt is undeniably there but for most applications is pretty negligible price to pay for the big wins. In practice, Clojurescript apps can often perform faster than similar apps built traditionally - especially for things like render optimization - immutable data enables cheap equality checks for memoization, it prevents unnecessary re-renders; data transform pipelines - transducers give you lazy evaluation, it's great for filtering/mapping through large datasets; caching - immutable data is safe to cache indefinitely, you don't have to worry about stale data;

You guys keep worrying about some theoretical "costs" - in practice, I have yet to encounter a problem that genuinely makes it so impossibly slow that Clojuresript just outright can't be used. Situations where it incurs a practical cost to pay are outliers, not a general rule.

[no_wizard]

> but for most applications is pretty negligible

Not all, and it is always preferable for it not to have a cost.

> I have yet to encounter a problem that genuinely makes it so impossibly slow that Clojuresript just outright can't be used

There’s a big swath of work that could benefit from the development streamlining that something like clojurescript or similar projects can give but any performance hit is deadly, like e-commerce.

There is also the fact that it doesn’t have 100% bindings to the raw JS and DOM APIs if I recall correctly, it’s often wrapped around React or assumed to be

[drob518]

> Also, experiencing immutability benefits in a mutable-first language can feel like 'meh'.

I felt that way in the latest versions of Scheme, even. It’s bolted on. In contrast, in Clojure, it’s extremely fundamental and baked in from the start.

[WolfOliver]

exactly, react could not deal with mutable object so they decided to make immutability seem to be something that if you did not use before you did not understood programming.

[iLemming]

React made immutability patterns more relevant which increased discussion of it. Some people did get preachy about it. Yet dismissing immutability entirely just because of that misses the entire point of why it's actually useful in managing complex state.

Have you ever thought about instead of having emotional reaction to obnoxious gatekeeping to learn about actual benefits of immutability?