iOS 14 Property Wrappers Unwrapped

iOS 14 Property Wrappers Unwrapped

Get to know one of the latest major features of Swift. It’s been some time since Swift acquired a pretty interesting feature called property wrappers. This feature is reputed to be designed mostly to facilitate SwiftUI and Combine API, so we (modern Swift developers ) had to face it immediately, with no time to start slowly and explore its guts.

It’s been some time since Swift acquired a pretty interesting feature called property wrappers. This feature is reputed to be designed mostly to facilitate SwiftUI and Combine API, so we (modern Swift developers ) had to face it immediately, with no time to start slowly and explore its guts.

But to be honest: Do all of us have a solid and deep understanding of how this feature is actually implemented and how it works?

For example, what makes it possible to set the [@State](https://developer.apple.com/documentation/swiftui/state)-marked property of a let constant (or of immutable self) without getting a Cannot assign to property error? Or let’s say, what’s the exact meaning of that cryptic $ prefix we use to fish the actual Publisher from the [@Published](https://developer.apple.com/documentation/combine/published) property?

If there’s still an air of mystery about it, let’s try to get to know it better. At first sight, the property wrappers feature may appear intimidating and more complicated than it really is. It may look like a black box doing something that can’t be done by any other means of Swift language.

But it’ll become much more tame once we understand this feature is nothing more than a shortcut to reduce boilerplate code when dealing with properties, a so called syntactic sugar. And it conceals as little compiler magic as possible. Let’s unwrap property wrappers and see them as transparent and straightforward.

Now, there are already tons of great articles providing various examples of concrete tasks property wrappers can solve. I’m not going to invent any more.

This series of 2-3 articles, the first of which you’re reading, aims rather to explain the intuition behind them and give a deeper view of their internal implementation, as well as some pitfalls and inborn limitations.

And finally, there are couple of recipes and best practices with this feature that I found useful and which I’d like to share. Hopefully, it’ll help you be more confident with your custom property wrappers code, as well as help you better understand their role in SwiftUI and Combine.

programming swift mobile xcode ios

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