A guide to hiring a Swift developer
Swift is the programming language Apple introduced for its platforms, and it is now open source. Most people meet it through iPhone apps, but it also runs on Mac, Linux and Windows. A Swift developer is someone whose strength is the language itself: how types fit together, how code stays safe and how a project stays easy to change. That skill matters more once your app is past its first release and many people touch the same files.
Language person or platform person
Hiring for a language is different from hiring for a platform. A platform role is about the whole product, including builds, store releases and how the device behaves. A language role is about the code. You may want the second when you already have people who handle releases, when you are building a shared package, when your code needs a clean up or when you want to run a Swift server. Many teams need both over time, and one person can often cover both. Know which one you are short of before you search.
Types, value semantics and clear modelling
Good Swift starts with the types. Structs and enums make data easy to copy and reason about, and classes are for things that have identity or shared state. An enum can describe the states of a screen so that impossible combinations cannot be written at all. Developers who model well write less defensive code and meet fewer odd bugs. Ask a candidate to explain a past choice between a struct and a class, and listen for reasons, not rules of thumb.
Optionals and error handling
Optionals make missing values part of the type, and they only help if the code respects them. Force unwrapping with an exclamation mark is a warning sign in most places. In the same way, errors should be thrown, caught and shown to the user in a sensible way, not swallowed. A careful Swift developer treats these as design questions, because that is where crashes and silent failures hide.
Protocols and generics
Protocols let you describe what a piece of code needs without tying it to one type, and generics let you write that code once. Used well, they make testing easy, because you can swap a real network client for a simple stand in. Used badly, they produce clever code nobody wants to read. A strong developer reaches for them when they remove duplication and stays with plain types when they do not.
Concurrency with async await
Swift has built in support for concurrent work. The async and await keywords let you write code that waits for a result in a straight line, and tasks and actors keep shared data safe. Newer language modes check for data races when you build. Many older projects still use completion handlers and queues, so a good developer can read both styles and move code over without breaking behaviour. Ask how they would cancel a request that is no longer needed, and how they keep work off the main thread.
SwiftUI and UIKit together
SwiftUI describes screens as a function of state, and UIKit is the older, more detailed framework underneath most existing apps. New projects lean on SwiftUI, but real apps often mix both for years. A Swift developer should be able to host a SwiftUI view inside a UIKit screen and the other way round, and explain where each shines. For the full app role, including releases and device work, see our iOS developers.
Swift on the server
Swift can run on Linux, which opens the door to writing server code in it. Vapor is an open source web framework for Swift, and there are others. The main appeal is one language for the app and the API, so models and validation can be shared. It is a smaller ecosystem than Node.js, Python or Java, so it makes the most sense when your team already lives in Swift. A developer who has done this can tell you honestly whether it fits your plans.
Packages and project structure
Swift Package Manager lets you split a project into small modules with clear edges. That keeps builds quicker, lets teams work without stepping on each other and makes code easier to reuse across an app, a widget and a server. A developer who has done this knows how to set the boundaries so that packages do not end up depending on each other in circles.
Testing Swift code
Code that is easy to test is usually code that is well designed. Swift developers use XCTest and the newer Swift Testing library for unit tests, and interface tests for the main journeys. The goal is quick feedback, so logic is kept out of views and outside services are hidden behind protocols. Ask how a candidate would test a function that calls the network, and how they keep tests from becoming flaky.
Moving from Objective-C
Many apps contain years of Objective-C. A full rewrite is rarely needed. A calmer path is to write new code in Swift, wrap the older parts with clear interfaces and replace the oldest or most painful pieces first. The two languages work in one project through bridging, so the app keeps shipping all the time. If your main need is to keep the older code healthy, our Objective-C developers can help, and often work next to a Swift hire.
When to hire a Swift developer
- You are starting a new Apple app and want the language done well from day one.
- Your Swift codebase has grown messy and slow to change.
- You want to adopt async await or move older callback code over.
- You want to split a big app into packages.
- You want a Swift server that shares code with your app.
If you need someone to own releases, device testing and the whole phone app, an iOS developer may be the better first hire, and you can add Swift depth later.
How to read a Swift developer’s background
Ask for code you can read, such as a shipped app, an open source package or a short sample. Look at how types are named, how errors are handled and whether the tests mean anything. Then ask the candidate to walk through one decision they would now make differently. People who can do that tend to keep improving the code, not only add to it.
Interview questions to try
- When would you pick a struct, a class or an enum for a new piece of data?
- How do you handle a failed network call so the user is not left guessing?
- What is an actor, and when would you use one?
- How would you move one Objective-C screen into Swift without breaking the app?
- How do you test code that depends on the network or the current time?
Good answers include a reason and a small example from real work. Be wary of someone who only repeats terms without a story behind them.
Run a small paid exercise
Give each finalist the same small task from your real work. It could be a data model with a few tests, a small package, a screen that loads data or the clean up of one messy file. Pay for the time. Then compare the code, the questions asked and how clearly each person explains the result.
Agree how the code is kept healthy
Agree on a style guide, a linter and how pull requests are reviewed. Keep the repository and your Apple developer account in your own name, with a separate login for each person. Ask for short notes on how to build and test the project from scratch. Then nothing is lost if the people change.
Settling in
Give your developer the repository, a test version of your server, the design files and one small first job. A weekly call and one shared task board keep progress easy to see. Share the odd corners of the code early, because that is where a specialist saves the most time.
Mistakes to avoid
- Hiring for a list of frameworks and never reading any of the candidate’s code.
- Letting force unwraps and large view files pile up.
- Rewriting working Objective-C just to have one language.
- Keeping the repository or the Apple developer account in a contractor’s name.
For more on this area, see our iOS developers for whole apps and our Objective-C developers for older code.