Remove swift-collections dependency by dfed · Pull Request #948 · livekit/client-sdk-swift

dfed · 2026-03-12T22:58:25Z

Summary

Replace DequeModule and OrderedCollections imports with minimal internal implementations (Deque, OrderedDictionary, OrderedSet) in Sources/LiveKit/Support/DataStructures/
Remove swift-collections from Package.swift, Package@swift-6.0.swift, and LiveKitClient.podspec
Unblocks consumers from being pinned to old swift-collections versions due to library evolution mode / XCFramework compatibility constraints

Details

The actual API surface used was tiny — 3 types, ~14 call sites, all internal. The new implementations are ~180 lines total, matching the existing pattern of lightweight data structures in the repo (RingBuffer, MapTable, TTLDictionary).

Test plan

xcodebuild build -scheme LiveKit -destination 'platform=macOS' succeeds
xcodebuild test -scheme LiveKit -only-testing LiveKitCoreTests -destination 'platform=macOS' — all non-E2E tests pass (E2E tests require local server)
CI passes

🤖 Generated with Claude Code

Package.swift

pblazej · 2026-03-17T10:37:23Z

Could you inspect the CI build errors? @dfed

Hint: the key is binary distribution (it was downgraded for a reason); the closest comment I could find was apple/swift-collections#546 (comment)

Haven't tested it tho

pblazej · 2026-03-17T13:12:27Z

After a short test, I see 2 obstacles:

newer versions do not officially support Swift 5.x toolchain (that won't be an issue soon)
more importantly, they rely on experimental features and will break library evolution mode, which is crucial for building a xcframework on top of LK - this is a strict requirement for us

I'm happy to merge it once we resolve the latter.

dfed · 2026-03-17T17:19:13Z

Got it. @pblazej would y'all be interested in a PR that copy/pasted the existing implementation of Deque, OrderedDictionary, and OrderedSet from Swift Collections as internal types such that y'all can remove swift-collections as a dependency? Ideally depending on LiveKit wouldn't restrict adopting apps from using the latest libs from Apple. Happy to update this PR

Replace DequeModule and OrderedCollections with minimal internal implementations covering only the APIs actually used (~14 call sites). This unblocks consumers from being pinned to old swift-collections versions due to library evolution mode compatibility constraints. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dfed · 2026-03-17T21:58:41Z

Sources/LiveKit/Support/DataStructures/Deque.swift

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2026 LiveKit


less sure about this. happy to put whatever you want up here

just run swiftformat over it, I think it's fine (checked on CI)

Array.removeFirst() is O(n), making the processSendQueue drain loop O(n²). Switch to a circular buffer backed by [Element?] with head pointer tracking for O(1) amortized append and removeFirst. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dfed · 2026-03-17T22:44:20Z

Sources/LiveKit/Support/DataStructures/Deque.swift

+/// A double-ended queue backed by a circular buffer.
+/// Provides O(1) amortized `append` and `removeFirst`.
+struct Deque<Element>: ExpressibleByArrayLiteral {
+    private var buffer: [Element?] = []


Minimal internal Deque using a circular buffer ([Element?] + head pointer). Provides O(1) amortized append and removeFirst, which matters because processSendQueue in DataChannelPair drains this in a tight while loop — an Array-backed implementation would make that O(n²).

Only implements the 4 APIs used: isEmpty, first, append, removeFirst, plus ExpressibleByArrayLiteral for = [] initialization.

For removeFirst you can leverage the % thing mentioned below, it was >40% faster in my case.

Sources/LiveKit/Support/DataStructures/OrderedDictionary.swift

Sources/LiveKit/Support/DataStructures/OrderedSet.swift

pblazej · 2026-03-18T07:23:39Z

@dfed thank you for going the extra mile here!

The problem with binary distribution is pretty common across Apple libs e.g. apple/swift-nio#2897 and already happened to use with swift-logging that we dropped vs bare OSLog.

I think porting the minimal API is better than carrying "a big part of the lib" under Apache as our usage is pretty narrow, the impact of future optimizations (leveraging ownership etc.) is probably negligible.

2 things:

please rebase on main to include Package@swift-6.2
you can run https://github.com/apple/swift-collections-benchmark against them to see if there are any bottlenecks vs the reference impl
- or I'll do it as a part of review - I'm talking mostly about DataChannelPair <- Deque

pblazej · 2026-03-18T10:41:54Z

collection-bench.zip

Attaching my results - nothing to worry about 🎉

The rest is micro-optimization like:

  // Before (integer division)
  let tail = (head + count_) % buffer.count

  // After (bitwise AND — same result when buffer.count is power of 2)
  let tail = (head + count_) & (buffer.count - 1)

pblazej · 2026-03-18T10:51:49Z

Sources/LiveKit/Support/DataStructures/Deque.swift

+    @discardableResult
+    mutating func removeFirst() -> Element {
+        guard count_ > 0 else {
+            fatalError("Cannot removeFirst from an empty Deque")


Suggested change

fatalError("Cannot removeFirst from an empty Deque")

preconditionFailure("Cannot removeFirst from an empty Deque")

matches Array

pblazej · 2026-03-18T10:53:20Z

Sources/LiveKit/Support/DataStructures/OrderedDictionary.swift

+        }
+    }
+
+    init(uniqueKeysWithValues keysAndValues: some Sequence<(Key, Value)>) {


I think the original does precondition here, I'm fine with in-place update as well, e.g.

init(uniqueKeysWithValues keysAndValues: some Sequence<(Key, Value)>) { for (key, value) in keysAndValues { if let i = index[key] { pairs[i] = (key, value) } else { index[key] = pairs.count pairs.append((key, value)) } } }

pblazej · 2026-03-18T11:04:37Z

Sources/LiveKit/Support/DataStructures/Deque.swift

+        if count_ == buffer.count {
+            grow()
+        }
+        let tail = (head + count_) % buffer.count


Since capacity is always a power of two (starts at 4, doubles)...

Suggested change

let tail = (head + count_) % buffer.count

let tail = (head + count_) & (buffer.count - 1)

pblazej · 2026-03-18T11:04:41Z

Sources/LiveKit/Support/DataStructures/Deque.swift

+        }
+        let element = buffer[head]!
+        buffer[head] = nil
+        head = (head + 1) % buffer.count


Suggested change

head = (head + 1) % buffer.count

head = (head + 1) & (buffer.count - 1)

pblazej · 2026-03-18T11:04:54Z

Sources/LiveKit/Support/DataStructures/Deque.swift

+        let newCapacity = max(buffer.count * 2, 4)
+        var newBuffer = [Element?](repeating: nil, count: newCapacity)
+        for i in 0 ..< count_ {
+            newBuffer[i] = buffer[(head + i) % buffer.count]
+        }


Suggested change

let newCapacity = max(buffer.count * 2, 4)

var newBuffer = [Element?](repeating: nil, count: newCapacity)

for i in 0 ..< count_ {

newBuffer[i] = buffer[(head + i) % buffer.count]

}

let newCapacity = max(buffer.count * 2, 4)

var newBuffer = [Element?](repeating: nil, count: newCapacity)

let mask = buffer.count - 1

for i in 0 ..< count_ {

newBuffer[i] = buffer[(head + i) & mask]

Update swift-collections package version range

9fa75ce

dfed commented Mar 12, 2026

View reviewed changes

Package.swift Outdated Show resolved Hide resolved

dfed and others added 2 commits March 12, 2026 15:58

Apply suggestion from @dfed

7387c03

Package@swift-6.0.swift too

8e7ea8b

hiroshihorie requested a review from pblazej March 17, 2026 10:28

dfed marked this pull request as draft March 17, 2026 17:56

dfed changed the title ~~Update swift-collections package version range~~ Remove swift-collections dependency Mar 17, 2026

dfed and others added 2 commits March 17, 2026 10:59

Add .changes entry for swift-collections removal

7c7cf98

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Remove redundant license line from attribution comments

60be12a

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dfed commented Mar 17, 2026

View reviewed changes

pblazej mentioned this pull request Mar 18, 2026

chore: update swift-collections and fix issues #952

Closed

pblazej reviewed Mar 18, 2026

View reviewed changes

	fatalError("Cannot removeFirst from an empty Deque")
	preconditionFailure("Cannot removeFirst from an empty Deque")

	let tail = (head + count_) % buffer.count
	let tail = (head + count_) & (buffer.count - 1)

	head = (head + 1) % buffer.count
	head = (head + 1) & (buffer.count - 1)

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2 participants

dfed commented Mar 12, 2026 •

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pblazej commented Mar 17, 2026 •

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