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submitted 2 months ago by lysdexic to c/programming

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[–] [email protected] 8 points 2 months ago (3 children)

..what? At least with Java Streams or Kotlin Sequences, they absolutely abort early with something like .filter().first().

[–] [email protected] 10 points 2 months ago (1 children)

Same in Python, Rust, Haskell and probably many others.

But apparently JS does work that way, that is its filter always iterates over everything and returns a new array and not some iterator object.

[–] nous 3 points 2 months ago* (last edited 2 months ago)

The old methods on Array will eagerly evaluate all elements. But JS has a new Iterator type with methods that works lazily instead.

[–] [email protected] 5 points 2 months ago (1 children)

Ya, streams may seem tedious (why do I have to call stream and collect?), but it’s like that for performance (and probably backwards compatibility).

If writing readable code is not peformant, then the language implementation needs to be fixed.

[–] [email protected] 5 points 2 months ago* (last edited 2 months ago) (1 children)

Honestly, it is much more code to use loop with non-local control like break, continue etc. (variable initialization, append, variable mutation in loops...) than just calling a collect function (which I assume just means to_list). In the above example, in most programming language I know, you don't even need to collect the result into a list.

Not to mention, large loops with non-local control is a breeding ground for spegatti code. Because you no longer have a consistent exit point to the loop, thus making the semantics hard o reason about.

In many languages, there are type class / trait / interfaces (whatever you want to call them) that allows lazy structures to share the same API as strict ones.

[–] [email protected] 3 points 2 months ago (1 children)

Yeah, in Java calling first() on a stream is the same as an early return in a for-loop, where for each element all of the previous stream operations are applied first.

So the stream operation

cars.stream()
    .filter(c -> c.year() < 1977)
    .first()

is equivalent to doing the following imperatively

for (var car : cars) {
    if (car.year() < 1977) return car;
}

Not to mention Kotlin actually supports non-local returns in lambdas under specific circumstances, which allows for even more circumstances to be expressed with functional chaining.

[–] nous 4 points 2 months ago (1 children)

These are not quite equivalent. In terms of short-circuiting yeah they both short-circuit when they get the value. But the latter is returning from the current function and the former is not. If you add a return to that first example then they are equivalent. But then cannot be used in line. Which is a nice advantage to the former - it can be used inline with less faff as you can just assign the return to a value. The latter needs you to declare a variable, assign it and break from the loop in the if.

Personally I quite like how the former requires less modification to work in different contexts and find it nicer to read. Though not all logic is easier to read with a stream, sometimes a good old for loop makes the code more readable. Use which ever helps you best at each point. Never blindly apply some pattern to every situation.

[–] [email protected] 4 points 2 months ago

Well yes, I was simplifying because I wanted to address the main (incorrect) criticism by @[email protected]. I agree with your comment

[–] [email protected] 1 points 2 months ago

@mbtrhcs @spartanatreyu well Java Streams try to, but it's not too hard to get them to accidentally process too much, or even blow up completely.

(This isn't a comment on coding styles or the article though)