I'm giving the overall idea a +0 and the specific proposal as currently
written a -1, because I think this is a much more complicated bikeshed
than it appears to be on the surface and the proposal doesn't begin to
address the issues. Specifically, I'm concerned about these points:
* `flatten` works on Optional<Optional<T>> and sequences of Optional<T>.
How does it make sense to rename these operations “join?”
Does it really? These don't work for me:
let x = [1,2,nil,4]
x.flatten()
let y = Optional(Optional(42))
y.flatten()
* The name and semantics of `flatten` is linked to that of `flatMap`.
It's almost impossible to explain what `flatMap` does without
reference to `flatten`. Will it make sense to explain `flatMap` in
terms of `joined`?
I think the current documentation comments do a pretty good job:
On the [T].flatMap(T -> U?) -> [U] version:
/// Returns an array containing the non-`nil` results of calling the given
/// transformation with each element of this sequence.
On the [T].flatMap(T -> [U]) -> [U] version:
/// Returns an array containing the concatenated results of calling the
/// given transformation with each element of this sequence.
(This one also mentions array.map(transform).flatten(), which would become
array.map(transform).joined().)
* `flatten` is a functional term of art in the same family as `flatMap`.
We have good reasons to consider changing some of the other names in
this family, such as `filter` and `reduce`, but that idea has met with
significant resistance on the list. How far should we go? Does it
make sense to make this one change alone?
I wouldn't argue for renaming flatMap. I'm not suggesting to change the
name of flatten() because I don't like it (I do); I'm suggesting to change
it because — unlike Ruby, whose Array has #flatten and #join, but the
latter is *only* for producing strings — we seem to have the *same*
functionality behind 2 differently-named APIs.
(Actually I feel like flatMap is a more fundamental functional method in
the family of filter and reduce than flatten/joined is. flatten is just
flatMap({$0}), although as pointed out above, flatten isn't actually
available in all the places that flatMap({$0}) would work.)
Jacob
···
On Mon, Jul 25, 2016 at 1:11 PM, Dave Abrahams via swift-evolution < swift-evolution@swift.org> wrote:
