When is .forEach {} preferred, vs java-style for loop? It looks like both get support from the lang...

# getting-started

[Jonathan Ellis]

When is .forEach {} preferred, vs java-style for loop? It looks like both get support from the language, e.g. destructuring for loop values

[Francesc]

forEach uses an iterator, so if you care about that (you need your loop to be as performant as possible), then you should use the for loop, otherwise it's a matter of preference.

[Ruckus]

forEach is inlined and uses a for loop, so it should only use an iterator when for uses an iterator. forEach is a tail function call, so it is often preferable for working with flows and pipelines. It does not support things like break and continue however, but from my experience those don't often play well with flows and pipelines anyway, as there would usually be some sort of filter or something earlier in the pipeline to account for it.

[Ruckus]

For just a simple "I need to loop over this collection and do stuff with the elements", generally prefer for. For anything more complex involving multiple steps, forEach makes a good step in the chain.

[ephemient]

IMO: only use forEach when it is meaningfully more useful, e.g.

foo["bar"]?.forEach { ... }

is more work to express with for. but otherwise use for

[ephemient]

it should only use an iterator when

@Ruckus not true; it always uses an iterator because that's resolved before inlining happens. e.g.

for (i in 1..10) {} // compiler optimizes this to an increment
(1..10).forEach {} // constructs range object, iterator, and boxes

[Jonathan Ellis]

TIL, thanks all!

[mkrussel]

For the Kotlin coding conventions.

Prefer using higher-order functions (filter, map etc.) to loops. Exception: `forEach`(prefer using a regular for loop instead, unless the receiver of forEach is nullable or forEach is used as part of a longer call chain).

https://kotlinlang.org/docs/coding-conventions.html#loops

[Ruckus]

@ephemient Interesting, I thought I remembered that being included in the compiler intrinsics. That's good to know, thanks.