Swift’s Sendable and @Sendable closures
Why you mess me up so bad?
Ah, Swift 5.7. I knew you’d have something to make me think about. The @Sendable protocol ultimately has meant that I’ve written a new network client for myself!
*So what is Sendable, @Sendable and why should we care*
Sendable types are safe to share concurrently.
Many different kinds of types are Sendable:
- Value types (because each copy is independent)
- Actor types (because they synchronise access to their mutable state)
- Immutable classes
- Internally-synchronized classes (for example with a lock)
- @Sendable function types
Sendable describes a common but not universal property of types.
The background
I had an old network library that I used to use. Suddenly it stopped working right around the time that Swift 5.7 got released. Didn’t seem to be a coincidence and it’s the fact that the dataTask function now has @Sendable it it’s signature+. Here is the commit where I fixed that!
Now, this is the article that explains @Sendable
