[SR-6691] Sequence.split should have a Lazy equivalent

[airspeedswift]

Previous ID	SR-6691
Radar	None
Original Reporter	@airspeedswift
Type	New Feature
Status	In Progress
Resolution

Additional Detail from JIRA

Votes	4
Component/s	Standard Library
Labels	New Feature, StarterBug, StarterProposal
Assignee	None
Priority	Medium

md5: 1e8d36124b9916625ca75e3f19b449dc

Issue Description:

Sequence.split is eager, but if you are splitting a collection, it should be possible to do it lazily. This could be done via an extension to LazyCollectionProtocol so you could write "a.b.c".lazy.split(separator: ".").

[swift-ci]

Comment by Daryle Walker (JIRA)

It seems this bug may have been inspired by the blog post "Conditional Conformance in the Standard Library". On a Swift mailing-list thread, I had a conversation with the author over a similar class. In my final code, I wrote:

• An iterator that chunks another

• A sequence that chunks another

• A sequence that chunks a collection

• A collection that chunks another

The blog only has something like the last one. But all four may be useful when porting to the standard library. (The first two types vend an Array of Element, the latter two SubSequence.)

Edit: looking at the blog post again, I noticed that his example splits on a given separator value, while my code splits after a set count of elements.

Edit 2: He does mention a chunking collection at the end of the blog post.

[swift-ci]

Comment by Tapan Thaker (JIRA)

CTMacUser (JIRA User) : Based on your comment shall I sure that you are working on this ?
I wanted to start contributing to Swift so thought this started task would be apt for me to get started.

[swift-ci]

Comment by Daryle Walker (JIRA)

I came up with the idea to help break up a Mac-specific collection (NSData), then for play. I wasn't thinking of it as a Swift standard library contribution. I don't know what to do here because I'm distracted by another Swift idea (which happens to me a lot). So, if you want to work on chunking (and/or splitting) yourself, go ahead.

[greenthings]

May i handle this issue?

please assign to me, I'll work on it and create a pull request!

[AnthonyLatsis]

@greenthings Please note that this feature needs a Swift evolution proposal.

[greenthings]

@AnthonyLatsis

Ok, thank you.

I'm going to make a proposal soon.

[injae-kim]

swiftlang/swift-evolution#2193

FYI, @greenthings make swift-evolution proposal~ I really want this sequence.lazy.split feature. thanks!

[greenthings]

Hi, @AnthonyLatsis , @airspeedswift

I have submitted a proposal for introducing lazy evaluation in Swift's Sequence. While the initial request was for implementing laziness in Sequence, I noticed that both Sequence and Collection could benefit from this feature. I'd appreciate guidance on whether I should create two separate proposals for 'Lazy Sequence' and 'Lazy Collection' or pursue a different approach."

Proposal URL:
swiftlang/swift-evolution#2193

[AnthonyLatsis]

Hi Jun, a single proposal is fine. I assume your proposal is not ready for official review yet. Please turn swiftlang/swift-evolution#2193 into a draft pull request until then.