Add iterator slice helpers by juliazadorozhnaya · Pull Request #791 · samber/lo

juliazadorozhnaya · 2026-01-30T20:07:28Z

This PR is a follow‑up to the previous slice‑helpers PR. It adds iterator versions of Take, TakeWhile, and TakeFilter along with tests, examples, and docs.

codecov · 2026-01-30T20:08:26Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.36%. Comparing base (b6d1bf3) to head (c36b4b1).
⚠️ Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #791      +/-   ##
==========================================
+ Coverage   94.26%   94.36%   +0.09%     
==========================================
  Files          18       18              
  Lines        2860     2891      +31     
==========================================
+ Hits         2696     2728      +32     
  Misses        149      149              
+ Partials       15       14       -1

Flag	Coverage Δ
unittests	`94.36% <100.00%> (+0.09%)`	⬆️

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d-enk · 2026-01-31T08:14:04Z

+// Tee duplicates the stream into multiple output channels without blocking.
+// If an output channel is full or not ready, the value is dropped for that channel.
+func Tee[T any](count, channelsBufferCap int, upstream <-chan T) []<-chan T {


In my opinion, this function is too specific.

Do you mean we should remove Tee because FanOut/FanIn already cover this, or keep it as a separate helper?

I agree with @d-enk .

Please open a new PR for further discussion.

Also: I would rename it in something more similar to FanOut: FanOutBestEffort, FanOutNonBlocking, FanOutLossy, FanOutDrop, FanOutFireAndForget, other ?

Done. I've removed the Tee function and all references to it from this PR.

…ding step

d-enk · 2026-02-21T09:15:02Z

I still find channel functions questionable.

I suggest splitting the pull request into two parts.

As it should have been from the beginning

d-enk · 2026-02-21T09:18:46Z

Just as I already suggested in a private message, I propose to split Sliding explicitly

switch {
case step == size:
...
case step < size:
...
case step > size:
...
}

samber · 2026-02-21T18:58:00Z


+// TakeFilter filters elements and takes the first n elements that match the predicate.
+// Equivalent to calling Take(FilterI(...)), but more efficient as it stops after finding n matches.
+func TakeFilter[T any, I ~func(func(T) bool)](collection I, n int, predicate func(item T, index int) bool) I {


Can you rename it to TakeFilterI and add a TakeFilter variant please?

(also in error below + doc)

Done. Renamed to TakeFilterI and added a TakeFilter variant.

samber · 2026-02-21T21:26:43Z

+// Tee duplicates the stream into multiple output channels without blocking.
+// If an output channel is full or not ready, the value is dropped for that channel.
+func Tee[T any](count, channelsBufferCap int, upstream <-chan T) []<-chan T {


I agree with @d-enk .

Please open a new PR for further discussion.

Also: I would rename it in something more similar to FanOut: FanOutBestEffort, FanOutNonBlocking, FanOutLossy, FanOutDrop, FanOutFireAndForget, other ?

juliazadorozhnaya · 2026-02-23T11:18:21Z

Just as I already suggested in a private message, I propose to split Sliding explicitly
switch {
case step == size:
...
case step < size:
...
case step > size:
...
}

Done. Sliding now uses an explicit switch on offset (step - size) for the three cases.

d-enk · 2026-02-23T14:44:08Z

I'd remove Distinct/DistinctBy too.

You can also clean up the title/commits.

d-enk · 2026-02-23T14:58:38Z

Can you rename it to TakeFilterI and add a TakeFilter variant please?

@samber Something went wrong somewhere

lo/slice.go

Line 12 in 921fb61

    
           func Filter[T any, Slice ~[]T](collection Slice, predicate func(item T, index int) bool) Slice {

lo/slice.go

Line 653 in 921fb61

    
           func TakeFilter[T any, Slice ~[]T](collection Slice, n int, predicate func(item T, index int) bool) Slice {

lo/slice.go

Line 713 in 921fb61

    
           func FilterReject[T any, Slice ~[]T](collection Slice, predicate func(T, int) bool) (kept, rejected Slice) {

juliazadorozhnaya · 2026-02-23T15:22:37Z

Can you rename it to TakeFilterI and add a TakeFilter variant please?

Something went wrong somewhere

lo/slice.go

Line 12 in 921fb61

func Filter[T any, Slice ~[]T](collection Slice, predicate func(item T, index int) bool) Slice {

lo/slice.go

Line 653 in 921fb61

func TakeFilter[T any, Slice ~[]T](collection Slice, n int, predicate func(item T, index int) bool) Slice {

lo/slice.go

Line 713 in 921fb61

func FilterReject[T any, Slice ~[]T](collection Slice, predicate func(T, int) bool) (kept, rejected Slice) {

Done. In slice.go renamed to TakeFilterI and added TakeFilter variant

juliazadorozhnaya · 2026-02-23T15:22:51Z

I'd remove Distinct/DistinctBy too.

You can also clean up the title/commits.

Done

d-enk · 2026-02-23T16:37:51Z

Done. In slice.go renamed to TakeFilterI and added TakeFilter variant

#791 (comment)

This was not a call to action for you...

samber · 2026-02-23T19:17:18Z

Oops, sorry. You wrote Take(FilterI(...)) so that why i suggested TakeFilterI but lets use TakeFilter instead. Sorry for the mistake.

EDIT: I reverted the last commit.

EDIT2: Thanks to both of you. I'm targeting a new release this week.

This reverts commit 6d2fcdc.

d-enk · 2026-02-23T21:21:20Z

I completely missed that Take(Filter()) already exists

As if TakeFilter() were redundant for sequences...

add iterator slice helpers and channel dedup/tee

ed15ab0

d-enk reviewed Jan 31, 2026

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Comment thread it/seq.go Outdated

d-enk reviewed Jan 31, 2026

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Comment thread channel.go Outdated

d-enk reviewed Jan 31, 2026

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note unbounded memory growth in Distinct; simplify Take

5da04ca

d-enk reviewed Feb 2, 2026

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Comment thread it/seq.go Outdated

d-enk reviewed Feb 2, 2026

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Comment thread it/seq.go Outdated

juliazadorozhnaya added 3 commits February 2, 2026 22:05

avoid extra iteration in Take/TakeWhile/TakeFilter and precompute Sli…

d303386

…ding step

avoid reallocations in Sliding overlap shift

baf3460

sliding uses ring buffer

1c8b999

juliazadorozhnaya marked this pull request as draft February 8, 2026 13:31

refactor Sliding and expand TestSliding

c36b4b1

juliazadorozhnaya marked this pull request as ready for review February 20, 2026 17:36

samber reviewed Feb 21, 2026

View reviewed changes

Remove Tee; add TakeFilter variant, rewrite Sliding

c2fc97e

juliazadorozhnaya added 2 commits February 23, 2026 18:14

remove channel Distinct/DistinctBy

23fa14d

TakeFilter/TakeFilterI for slice

6d2fcdc

juliazadorozhnaya changed the title ~~Add iterator slice helpers and channel distinct/tee utilities~~ Add iterator slice helpers Feb 23, 2026

samber added 2 commits February 23, 2026 20:21

Revert "TakeFilter/TakeFilterI for slice"

0956bcb

This reverts commit 6d2fcdc.

doc add new helpers to llms.txt

0ab6666

samber merged commit c1d11cb into samber:master Feb 23, 2026
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