Rust for JavaScript Developers – Functions and Control Flow

Re:Rust for JavaScript Developers – Functions and Control Flow by 65536 on Sunday July 05, 2020 @11:28PM (#23744416)

Speaking of which, coming from Rust (well, when I say it like that it sounds like Rust is the only language I ever used which is of course not true. I think Rust as a first language would be highly unusual still), I enjoyed being able to say

Rust code:

    let foo = if x <= 0
    {
        0
    }
    else if something_else > 50
    {
        9000
    }
    else
    {
        42
    };

And I miss this in Swift.

The ternary operator is fine on its own but I’m not a huge fan of nested ternary operators. With a bit of whitespace it's somewhat readable still but still not as comfortable and easy to read correctly.

Swift code:

    let foo = x <= 0 ?                0 :
             (somethingElse > 50 ? 9000 :
                                     42 )

One way of writing something that is more similar to the way I'd write it in Rust would be to make a closure and then run it.

Swift code:

    let foo =
    { () -> Int in
        if x <= 0
        {
            return 0
        }
        else if somethingElse > 50
        {
            return 9000
        }
        else
        {
            return 42
        }
    }()

But it's a bit annoying still, both to read and to write. Also, even in the current version of Swift (Swift 5), the compiler cannot infer the return type of the closure on its own even though all of the branches return an Int, so I'd have to explicitly annotate that as I have done in the code above.

I guess for a lot of people they would just make foo mutable and write the code as

Swift code:

    var foo = 42
    
    if x <= 0
    {
        foo = 0
    }
    else if somethingElse > 50
    {
        foo = 9000
    }

I concede that this is probably the most readable out of all of the three Swift code samples in my comment. But the point is that I didn't want foo to be mutable. I wanted to assign a value to it based on some simple logic and have it be immutable.

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Re:Rust for JavaScript Developers – Functions and Control Flow by bobbylarrybobby on Monday July 06, 2020 @12:45AM (#23744771)

I find ternary operators perfectly readable if you split the parts across lines — they map exactly to the conditions and statements in an if-else group.

    Cond1 // if this
    ? Result1 // return this
    : cond2 // else if this
    ? Result2 // return this
    : cond3 // else if this
    ? Result3 // return this
    : ResultElse // else return this

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Re:Rust for JavaScript Developers – Functions and Control Flow by mekkkkkk on Monday July 06, 2020 @06:13AM (#23746297)

I've come to hesistently accept nested ternaries, but I try to have all lines lead with a colon. This kinda mimics a switch statement with returns.

  firstPossible ? thenThis
    : secondPossible ? thenThisOtherThing
    : thirdPossible ? thenThisThirdThing
    : defaultThing

Always fun to see how people treat ternary nesting. They still feel a bit naughty to me. The terseness is sort of unbeatable though.

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Re:Rust for JavaScript Developers – Functions and Control Flow by Kkoala on Monday July 06, 2020 @08:48AM (#23747296)

It's funny how people have so many different preferences for ternary formatting. I can't think of any other operator that would have tens of different format prefs.

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Re:Rust for JavaScript Developers – Functions and Control Flow by pests on Monday July 06, 2020 @02:11AM (#23745165)

Which is not true in PHP up until the most recent version (iirc) due to it being left associative instead of right associative you are assuming.

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Re:Rust for JavaScript Developers – Functions and Control Flow by amenod on Monday July 06, 2020 @02:11AM (#23745167)

True, or even:

    Cond1 // if this
      ? Result1 // return this
      : cond2 // else if this
        ? Result2 // return this
        : cond3 // else if this
          ? Result3 // return this
          : ResultElse // else return this

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Re:Rust for JavaScript Developers – Functions and Control Flow by giantDinosaur on Monday July 06, 2020 @05:02AM (#23745964)

Goodness me that has potential to become something truly hideous.

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Re:Rust for JavaScript Developers – Functions and Control Flow by amenod on Monday July 06, 2020 @01:11PM (#23749998)

It's actually not that bad in practice... But I guess the pragmatic formatting is "whatever `prettier` does by default" anyway. :)

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Re:Rust for JavaScript Developers – Functions and Control Flow by Kkoala on Monday July 06, 2020 @08:46AM (#23747285)

It's funny how people have so many different preferences for ternary formatting. I can't think of any other operator that would have tens of different format prefs.

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Re:Rust for JavaScript Developers – Functions and Control Flow by skocznymroczny on Monday July 06, 2020 @02:48AM (#23745336)

I dislike the ternary operator in languages like C++. And many languages copy-paste it because they are used to it. I much prefer the more literal and reversed form in Python.

Instead of:

int salary = isEmployed() ? 2000 : 0

I prefer:

int salary = 2000 if isEmployed() else 0

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Re:Rust for JavaScript Developers – Functions and Control Flow by JimDabell on Monday July 06, 2020 @04:13AM (#23745731)

Yes, it also makes the larger example somewhat readable:

    func calculate_tax(income):
        return 0 if income < 10 else 20 if income < 50 else 50

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Re:Rust for JavaScript Developers – Functions and Control Flow by jfkebwjsbx on Monday July 06, 2020 @09:11AM (#23747487)

I love that idea, but I still prefer it’d read the same as an if. Meaning the condition first and the false case last.

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Re:Rust for JavaScript Developers – Functions and Control Flow by nicoburns on Monday July 06, 2020 @10:04AM (#23747942)

Rust implements this:

    let foo = if is_employed() { 2000 } else { 0 }

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Re:Rust for JavaScript Developers – Functions and Control Flow by w-ll on Sunday July 05, 2020 @11:34PM (#23744450)

I'd guess i fall into the mutable camp, while sometimes doing a closure.

Nested ternary if statements scare me from my PHP days, and noticed inlined closures can at times be harder to grok at a glance.

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Re:Rust for JavaScript Developers – Functions and Control Flow by hardwaregeek on Monday July 06, 2020 @01:09AM (#23744901)

Agreed. Plus if the else clause has a side effect, you can't assign it to the variable, which means you need to instantiate to null or a dummy value. Very messy.

What's funny is that expression oriented languages translate really nicely to stack VMs. My hobby language compiles down to WASM and it was almost trivial to code gen if expressions.

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Re:Rust for JavaScript Developers – Functions and Control Flow by jurip on Monday July 06, 2020 @03:46AM (#23745614)

Agreed about missing if and switch expressions in Swift. My preferred way of writing that would be:

    let foo: Int
    if x <= 0 {
        foo = 0
    } else if somethingElse > 50 {
        foo = 9000
    } else {
        foo = 42
    }

That way you get immutable foo and the compiler will shout at you if you forget to assign the value in one branch. It's not quite as nice as an expression, but it's less punctuation than the closure and the result is just as safe.

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Re:Rust for JavaScript Developers – Functions and Control Flow by GrayShade on Monday July 06, 2020 @10:25AM (#23748218)

It's probably not the most idiomatic thing, but in Rust you can write:

    let foo = match () {
        _ if x <= 0 => 0,
        _ if something_else > 50 => 9000,
        _ => 42,
    };

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