Why some functions in stdlib start with a capital ...

# stdlib

[Dmitry Kandalov]

Why some functions in stdlib start with a capital letter when the name matches return type (as described in the coding conventions) but some don’t? For example, uppercase List but lowercase `sequence`:

List(size = 1) { "foo" }
sequence { yield("foo") }

[Marc Knaup]

sequence is a builder/DSL. List is simply passed a constructor parameter that is called for each index.

[Dmitry Kandalov]

DSL or not they are both functions:

public inline fun <T> List(...): List<T> = ...
public fun <T> sequence(...): Sequence<T> = ...

[ephemient]

I don't know if this is the reason, but:
List(n) { ... } is clearly a constructor or function invocation
Runnable { ... } is clearly a lambda
sequence { ... } is clearly a function invocation
if it were Sequence { ... }, that is not so clear

[Jordan Stewart]

That does make a lot of sense. kotlin/collections/Sequences.kt contains the following though--

public inline fun <T> Sequence(crossinline iterator: () -> Iterator<T>): Sequence<T> = object : Sequence<T> {
    override fun iterator(): Iterator<T> = iterator()
}

e.g. the implementation of fun sequence(..) is just Sequence { iterator(block) }, calling fun Sequence(..) — this is the one which I’m most curious about!

[Jordan Stewart]

(I mean the answer might be that it’s a wordy way of making interface Sequence into effectively fun interface Sequence, but why guess when you can ask? 🙂)

[Dmitry Kandalov]

@ephemient

List(n) { ... } is clearly a constructor or function invocation

Yes.

Runnable { ... } is clearly a lambda

Not unless you know that Runnable is a functional interface, so I wouldn’t say “clearly” 😉

sequence { ... } is clearly a function invocation

Yes. The question is why make it clearly a function and also have fun Sequence(){...}. It would be a more consistent coding style in stdlib to capitalise all functions if they have the same name as returning type.

[ephemient]

I didn't realize fun Sequence() was public, but it acts constructor-like while sequence() acts builder-like, it doesn't feel like the same thing

[ephemient]

now I do think it would be nice to have all the builders named similarly, e.g. stdlib's buildString { ... } buildList { ... } etc., but there was a community poll a little while back where people seemed to mostly prefer the non-build-prefixed names so...

[Marc Knaup]

https://youtrack.jetbrains.com/issue/KT-26678