CODEWITHSUNDEEP
ioscswiftfunction-pointers
lys
lys

Reputation: 1027

Using Function pointer callback methods in Swift

I'm seeking to better understand how imported C functions like this can be implemented in Swift. This error message is helpful, but I've tried many variations of this as params in the swift function and can't quite get it.

Cannot convert value of type '() -> ()' to expected argument type 'method_handler?' (aka 'Optional<@convention(c) (Optional<UnsafeMutablePointer<msg_data>>, Optional<UnsafePointer>, Optional<UnsafeMutablePointer<Optional<UnsafeMutablePointer>>>, Int32, Optional) -> ()>')

typedef void (*method_handler)(const msg_data_ptr msg, const char *types,
                                   arg_ptr *argv, int argc, void *user_data);

func handler(args)
{
    for (i, arg) in args.enumerated() {
        print("argument \(i) is: \(arg)")
    }
}

passed in here:

add_handler_new("handler", &handler, nil, 0, 1);

Upvotes: 2

Views: 556

Answers (1)

Eugene Dudnyk
Eugene Dudnyk

Reputation: 6030

As the error message says, you have to use @convention(c) in order to define the swift function or closure that is interoperable with other C functions. Try this:

typealias MethodHandler = @convention(c) (
        _ msg_data_ptr : UnsafeMutablePointer<msg_data>?, 
        _ types: UnsafePointer<Int8>?, 
        _ argv : UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>?, 
        _ argc: Int32, 
        _ user_data: UnsafeMutablePointer<Int8>?
    ) -> Void


let handler: MethodHandler = { msg_data_ptr, types, argv, argc, user_data in
    ...
}

add_handler_new("handler", handler, nil, 0, 1)

Upvotes: 1

Related Questions