for vs forEach

[mikehearn]

For loops vs forEach - two very similar constructs with very similar syntaxes:

for (foo in foos) { foo.thing() }

vs

foos.forEach { it.thing() }

I prefer the traditional for form, seeing as that's what forEach becomes anyway and it encourages you to pick a more meaningful iterator name than it, but I'm happy with either.

Suggested rule: use forEach only as the terminal operation of a chain of functional operations (map, filter, groupBy, etc). Don't use a variable name followed by .forEach { } instead of a for loop.

[cypressious]

Use collection?.forEach {} if the collection is nullable.

Prefer for over forEach if you need to use break. As continue can be emulated by return@forEach, using it in either is fine.

[voddan]

I personally like using forEach if the operation I need to perform is short, like printing the element:

names.forEach {println(it)}
//or
names.forEach(::println)

I don't see a problem with forEach unless people try to do break or continue and invent "cleaver" workarounds

[cypressious]

Good point. Function references obviously lend themselves very well to being used with forEach.

[mikehearn]

The function is more flexible, for sure. I'd also be OK with just standardising on "use forEach everywhere". It's more the consistency issue that's a pain.

[mahozad]

I think Item 46 and also Item 45 from Effective Java (3rd Edition) may be relevant to this discussion.

[cable729]

Based on the readme, guidance on for vs forEach should not have been moved to the official coding conventions reference:

Issues where a sufficient amount of consensus has been reached are closed, and the rules are moved to the official style guide at https://kotlinlang.org/docs/reference/coding-conventions.html.

I recommend removing it from the coding conventions until a consensus has been reached.