A Swift macro that makes it dead simple to execute something just once.
Sometimes you want to ensure a piece of code only runs once—no matter how many times it's called. That’s what #once is for.
Just wrap your code in a #once block, and Swift will take care of the rest:
#once {
print("Doesn't matter how many times this is called, it'll only be printed once")
}This is useful for:
- One-time side effects (e.g. analytics, logging)
- Lazy initialization in non-global contexts
- Ensuring swizzling or other runtime setup runs exactly once
- Basically anything you only want to trigger just once
No need for custom flags, static vars, or DispatchOnce-style wrappers. Just write your code where you want it to run once, and be done with it.
Thread-safe and works with async code.
Add the package via Swift Package Manager:
.package(url: "https://github.com/davdroman/swift-once-macro", from: "1.0.0"),.product(name: "Once", package: "swift-once-macro"),Then import and use:
import Once
#once {
// executes once, ever
}That's it.