How can method in Swift with inout parameter be used in Objective-C?

Question

I want

func foo(inout stop: Bool) -> Void {
    // ...
}

use in my Objective-C part. But it is never generated in Module-Swift.h header. If I mark it with @objc, the

Method cannot be marked @objc because the type of the parameter cannot be represented in Objective-C

error occurs.

Answer 1

You can't use an inout parameter when bridging with Objective-C, but you can do something similar if you use an UnsafeMutablePointer<T> (T would be Bool in your case). It would look something like this:

@objc func foo(stop: UnsafeMutablePointer<Bool>) -> Void {
    if stop != nil {
        // Use the .pointee property to get or set the actual value stop points to
        stop.pointee = true
    }
}

---

Example

TestClass.swift:

public class TestClass: NSObject {
    @objc func foo(stop: UnsafeMutablePointer<Bool>) -> Void {
        stop.pointee = true
    }
}

Objective-C:

TestClass *test = [[TestClass alloc] init];
BOOL stop = false;
[test foo:&stop];
// stop is YES here

Answer 2

Similarly to what happening with generics, inout is not objc-compatible.

One possible workaround is to embed your parameter(s) in a class (which is a reference type, hence passed by pointer and not by value):

@objc class MyFuncParams {
    var stop: Bool

    init(stop: Bool) {
        self.stop = stop
    }
}

and define the function to accept an instance of that class:

func changeParam(params: MyFuncParams) {
    params.stop = true
}

Not an elegant way to solve the problem, but what's important is that it should work (never tried myself though).