When is nesting good or neutral?

I was reading this post...

Please don't nest promises

Basti Ortiz ・ Jan 6 '20

#javascript #node #programming #tips

And I think we can generally agree on the idea here.

It got me wondering where nesting isn't bad, because in a lot of situations, nesting is a problem.

Is nesting in markdown a smell in and of itself?

<section>
  <div>
    <div>
      <div>
        ...

Is this good or neutral or is it something to be avoided when possible?

Is nesting conditional logic always bad, or are there situations where it's more helpful?

This is broad and abstract, so feel free to take it in any direction.

Comments

[Basti Ortiz]

If you don't mind, I'll "repost" my reply to you from the article in question. 😉

Basti Ortiz (Some Dood)

Jan 6

Hmm... that's a good question. To that I will argue no, there is no such thing as a "good kind of nesting" in any programming language, even for markup.

I would like to expound on the specific case of HTML because deeply nested markup can be an indication of a poorly planned layout structure teeming with so-called "CSS hacks". On the discussion of performance, deeply nested markup also takes it toll on the amount of memory the DOM consumes. All those wrapper divs may seem innocent at first, but having a bunch of them will definitely be taxing for lower-end devices, especially on mobile.

For data-oriented nesting such as in XML and JSON, perhaps I can be more lenient, but even then, deeply nested markup requires a bunch of computer resources just to traverse, not even at the data processing stage yet.

[Dian Fay]

I'm kind of confused by the premise. Certainly one should avoid driving nails with the butt of a hacksaw if there's anything better to hand. That doesn't make hacksaws bad. Hierarchization and nesting are organizational tools; sometimes they suit, sometimes they don't.

[林子篆]

A few cases, sometimes we cannot extract out a function because the abstraction is bad for maintaining, however, we have a complex condition like: if a && b && c, in case I prefer if a { if b { if c {} else {} } else {} } else {}. But most of the time I can find out how to extract it as a new function, but if really cannot do that, simple-ugly is better than elegant-hiding-the-problem.

[Shivan Moodley]

When it comes to conditional logic, I always try to ask myself 'how important is readability for this code block' i.e is this something that would change as my project progresses, and further than that, am I the only maintainer of the code? If it is highly volatile code (subject to change often) and if I am not the sole maintainer, then I err on the side of rewriting nested conditionals. I don't think nested blocks are generally bad, but I can't think of a case where they outperform inversion of conditions to single statements, except I guess in terms of mental overhead.

So for instance I would tend to write this

function conditionalsOrNo() throws AnException {
    if (!codeIsNotVolatile) throws new YouShouldRefactorException()
    if (!codeIsMaintainedByMe) throws new WhyAreYouTryingToCauseYourselfPainException()
    return writeConditionals()
}

Instead of this

function conditionalsOrNo() throws AnException {
    if(codeIsNotVolatile) {
        if(codeIsMaintainedByMe) {
            return writeConditionals()
        } else {
            throws new YouShouldRefactorException()
        }
    } else {
        throws new WhyAreYouTryingToCauseYourselfPainException()
    }
}

So I guess the question is more down to the conditions the code exists in, rather than the immediate computational benefits of nested vs alternatives?

This is a really great question

[Lito]

And what about:

function conditionalsOrNo() throws AnException {
    if (!codeIsNotVolatile) {
        throws new YouShouldRefactorException();
    }

    if (!codeIsMaintainedByMe) {
        throws new WhyAreYouTryingToCauseYourselfPainException();
    }

    return writeConditionals();
}

Easy to read and no nested code.

[Shivan Moodley]

That works too. The lack of braces is just my lazy inner java dev showing

[Jon Bristow]

And now with monads....

fun conditionalsOrNo(maybeCode: Either<Error, Code>) = maybeCode.map(Code::writeConditionals)

Please note that this example is bad because it appears to rely on side effects

[Shivan Moodley]

I have googling to do it seems

[Jon Bristow]

Please note that the brevity of my example relies upon a strong type system with at least basic generics support.

Interesting google terms:

Discriminated Unions
Functional programming
Monads
Haskell (or Hindley-Milner type systems)
Lodash (decent javascript functional library, though this may be a little opaque unless you experiment with a FP language for a while)

[Shivan Moodley]

Thank you for this. I'll add it to this weekends reading list.

[HS]

It's (sometimes) horrible how frameworks/tool generate HTML but also necessary in some cases and not a big deal for developers as those tools handle those lines themselves. On the other hand if written by human it is something that should be avoided as much as possible.

1. readability
2. sometimes it's even performance issue but only in case of data structures (html,xml,json being included as some form of "data structure"), I don't see that many benefits

Reactive style made it possible to have no idea what you wrote last month, let alone last year. Now it can be written better etc but there's a reason async/await was added.

Although it's a bit uglier and harder to write. with microservices reactive style is good enough in terms of clearness as your code is split. Now a lot of people would go with Go (pun intended), Kotlin etc for those prefix_routines but

this.map(is -> is.standard()).flatMap(x -> "As many languages use same sytanx")

which is quite good when having more than 1 technology. Now you do write either more functions or less clear code and there's no "a matter of taste" in it as it turns out you can take a deep look at previous iterative codes and compare to reactive ones and the actual problem starts with nesting

result.flatMap(x -> anotherPublishFunction(x).map(y -> { y.setSomething("lalal"); return y })).zipWith(...)

If you try to write this more clearly you end up either with more lines or more functions which convert stuff, zip, publish, toIterrable etc.

You need to deal with complex/ugly code. You need to couple some stuff. You need iterative approach sometimes. You need nesting sometimes. It's just a thing we have to live with :D

[John Au-Yeung]

The less nesting the better.

It's jist so hard to read deeply nested code.

And I think the whole point if Promises is to eliminate callback hell, which is deeply nesting callbacks.

[Jason C. McDonald]

From a Python perspective, we are informed by the Zen of Python

Flat is better than nested.

Python provides many patterns that allow one to avoid nesting in most cases. Of course, it's not altogether unavoidable, but you should try to avoid going any deeper than 2-3 levels, functions included.

[Michiel Hendriks]

Without proper deep levels of nesting how can I post my hadoken gif?

[Ben Halpern]

😄

[Jesse M. Holmes]

This is the answer I came for. :)

[Paweł Kowalski]

Nesting when you write is very useful, given its obvious in your editor.

Nesting in output, probably not useful at all.

Nesting when writing logic, i would say, i try to do as little of that as possible, because parsing that in my brain is a chore.