Use statement For to write in a Tuple

问题

I use this code to send midi sysEx. It s perfect for sending "fix" data but now i need to send data with different size.

            var midiPacket:MIDIPacket = MIDIPacket()
            midiPacket.length = 6
            midiPacket.data.0 = data[0]
            midiPacket.data.1 = data[1]
            midiPacket.data.2 = data[2]
            midiPacket.data.3 = data[3]
            midiPacket.data.4 = data[4]
            midiPacket.data.5 = data[5]
            //... 
            //MIDISend...

Now imagine i have a String name "TROLL" but the name can change. I need something like this :

            var name:String = "TOTO"
            var nameSplit = name.components(separatedBy: "")
            var size:Int = name.count

            midiPacket.length = UInt16(size)

            for i in 0...size{
                midiPacket.data.i = nameSplit[i]
            }
            //...
            //MIDISend...

But this code don t work because i can t use "i" like this with a tuple. If someone knows how to do that.

Thanks in advance. KasaiJo

回答1:

C arrays are imported to Swift as tuples. But the Swift compiler preserves the memory layout of imported C structures (source), therefore you can rebind a pointer to the tuple to an pointer to UInt8:

withUnsafeMutablePointer(to: &midiPacket.data) {
    $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout.size(ofValue: midiPacket.data)) {
        dataPtr in // `dataPtr` is an `UnsafeMutablePointer<UInt8>`

        for i in 0..<size {
            dataPtr[i] = ...
        }
    }
}

回答2:

I don't know any proper way to do that, as tuples are compound type and can't be extended to add additional functionality.

One way of improving it I can think about is extracting it to a func like:

    func setMidiPacket(_ midi: MIDIPacket fromArray array: [ProbablyInt]) {
        midiPacket.length = 6
        midiPacket.data.0 = data[0]
        midiPacket.data.1 = data[1]
        midiPacket.data.2 = data[2]
        midiPacket.data.3 = data[3]
        midiPacket.data.4 = data[4]
        midiPacket.data.5 = data[5]
    }

setMidiPacket(midi, data)

来源：https://stackoverflow.com/questions/46972156/use-statement-for-to-write-in-a-tuple

标签

swift

for-loop

tuples