Why are non-sendable properties mutable from Tasks?

Using Swift
, ,
1

A lot of online resources say non-final classes are not Sendable by default. That means classes and their properties are not thread-safe. So why is this code not raising an error:

class Counter {
    var count = 0
    func increment() {
        count += 1
    }
}

class Tester {
    var counter = Counter()
    
    func mutate() {
        Task {
            counter.increment()
        }
    }
}

I was expecting an error to be raised at counter.increment() since counter isn't Sendable.

Can anyone tell why this code isn't raising an error?

2

If you set the strict concurrency checking flag, you'll get a warning here. Because of that, I'll assume this is by design and not a issue. Perhaps to support older code that lives outside the concurrency paradigm by default (?).