Agent skill · emilkowalski
write-swift
How to write modern Swift well — modeling with value types, Swift 6 data-race safety and approachable concurrency (@concurrent, main-actor-by-default, actors, task groups), protocols and generics (some vs any), API design, performance and ARC, Swift Testing, macros, and the modern language features agents don't know about yet. Use when writing, reviewing, or migrating Swift, or when a concurrency error, a hang, a data race, a retain cycle, or a performance problem needs fixing.
What it needs
About 12k tokens when loaded.
What this skill does
Write Swift Initial Response When this skill is first invoked without a specific question, respond only with: I'm ready to help you write modern Swift, the way the language wants to be written. Do not provide any other information until the user asks a question. How to write Swift the way the language wants to be written, current through Swift 6.4. Toolchain baseline: Swift 6.3 (current release as of August 2026). Everything here compiles on 6.3 unless marked ⚠, which flags unreleased Swift 6.4 features. Concurrency guidance assumes the Swift 6.2 model — if the project is on 6.1 or earlier, §3's rules about async and @concurrent do not apply. The through-line: Swift is a progressive-disclosure language. Start with the simplest, most static, most single-threaded thing that works, and buy dynamism — concurrency, reference semantics, existentials, unsafe pointers — only where you can point at the reason. Every rule below is an application of that. Model this hierarchy of defaults. Move down a level only with a reason you can state: Need Reach for Move down only when ------------ ----------------------- ---------------------------------------------------------- Data struct / enum you need identity, sharing, or inheritance Abstraction concrete type you have repeated code across types Polymorphism some P (generic) you need heterogeneous storage → any P Execution main actor, synchronous profiling shows a hang → async → @concurrent → actor Memory Array, String profiling shows the cost → InlineArray, Span Safety safe API C interop or a measured hot path → Unsafe --- 1. Model data with value types Value types are the default in Swift, not a special case. Default to struct and enum. Use class only for identity, shared mutable state, inheritance, or resource lifetime. A window, a database connection, an entity stored in a rendering engine — those have identity. A Point, a Drink, a Material does not. let by default; var only when you mutate. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills emilkowalski/write-swift