https://stackoverflow.com/q/78999607/1271826

ComplexData.swift

final class ComplexData: @unchecked Sendable {
    private let lock = NSLock()

    private var _name: String
    var name: String {
        get { lock.withLock { _name } }
        set { lock.withLock { _name = newValue } }
    }

    init(name: String) {
        _name = name
    }
}

As an aside, this pattern only works if the properties are not reference types with their own mutable properties. We’re OK with String, but if you add more properties, be wary of this limitation.

By the way, if you're worried about how hairy ComplexData might get with lots and lots of properties, you can abstract this synchronization logic out into a property wrapper:

@propertyWrapper
struct Synchronized<T>: @unchecked Sendable {
    private var _wrappedValue: T
    private let lock = NSLock()

    var wrappedValue: T {
        get { lock.withLock { _wrappedValue } }
        set { lock.withLock { _wrappedValue = newValue } }
    }

    init(wrappedValue: T) {
        _wrappedValue = wrappedValue
    }
}

final class ComplexData: @unchecked Sendable {
    @Synchronized var firstName: String
    @Synchronized var lastName: String

    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
}