---
title: "A deep dive into Collections, Sequences, and Iterators in Swift – Donny Wals"
url: https://daily.dev/posts/a-deep-dive-into-collections-sequences-and-iterators-in-swift-donny-wals-bbq8zop1r
source_url: https://www.donnywals.com/a-deep-dive-into-collections-sequences-and-iterators-in-swift/
type: article
source: "Donny Wals"
published: 2025-11-05T11:56:20.608Z
updated: 2025-11-05T11:56:42.135Z
tags: ["swift"]
reading_time: 11
upvotes: 0
comments: 0
language: en
---

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# A deep dive into Collections, Sequences, and Iterators in Swift – Donny Wals

**[Donny Wals](https://daily.dev/sources/donnywals)** · 11 min read · 0 upvotes · 0 comments

## Summary

Explores how Swift's iteration machinery works under the hood, from the basic Sequence and Collection protocols to their async counterparts. Explains how for-in loops desugar into iterator calls, why most iterators are structs with value semantics, and the pitfalls of mutating collections during iteration. Includes practical examples of implementing custom sequences and collections, plus guidance on bridging callback-based APIs to async streams using AsyncSequence.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://www.donnywals.com/a-deep-dive-into-collections-sequences-and-iterators-in-swift/>

---

Tags: [#swift](https://daily.dev/tags/swift)

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