[swift-evolution] Contiguous storage byte arrays

[Ted F.A. van Gaalen]

Hello Johan, thanks for your reply. 
It would be nice if there was some kind of attribute like
var bytes: [UInt8] contiguous  = ...      //  to declare a contiguous array. 

Ok then, I'd suggest creating a new Swift type with an internal fixed length
and contiguous byte array inside. Perhaps to be implemented in a Swift library.

This swift class example here is just a Model
 because to a programmer  [Swift any type]  arrays are undefined whether to be 
be contiguous or not.  No error handling is implemented in this examplel)

final class ByteArray   // Note: Just a model for a lower level implementation! 
{
    private var bytebuffer = [UInt8]()   // Not! Must be an internal contiguous byte array.
    
    init(contents: [UInt8])  // Constructor.
    {
        for byte in contents                  // load bytes into contiguous!! buffer
        {
            bytebuffer.append(byte)
        }
    }
    
    func setByte(index index: Int, byte: UInt8)     // set a byte in the buffer
    {
       if index.outsideRange(0..<bytebuffer.count)  // should be valid index
       {
          // Aarrggh! throw: subscripting error
       }
       bytebuffer[index] = byte
    }

    // other functions could be added to clear, shift etc.
    
    func address() -> Any
    {
        return bytebuffer //  use as someExternalFunc(bytes.address,…) 
    }

    func length() -> Int
    {
        return bytebuffer.count
    }
}
 

// usage example:  

let bytes = ByteArray(contents:   someUInt8array )

// or -other constructor-  make a byte array of 512 zero bytes:

let bytes = ByteArray(length: 512, fillWith: 0) 

bytes.setByte(index: 0, byte: midiCommandByte)
bytes.setByte(index: 1, byte: midiStatByte)

// define subscriptors? so that we could just write:  bytes[idx] = value

var offset = 2       // load databytes
for b in midiData
{
    bytes.setByte(index: offset, byte: b)
   offset++                    
}   


// pass the address of the contiguous byte buffer within (this instance of) ByteArray to some external function:

someExternalFunc(&bytes.address, . . . ) 



Regards
Ted

> On 14.02.2016, at 20:26, Johan Jensen <jj at johanjensen.dk> wrote:
> 
> 4 Tuples:  please take a look at this code:  
> 
>  static var z: UInt8 = 0  // initalize tuple with 256 UInt8 values, bytes:
>     
>     // Silly: why not an array instead of this.. a tuple is needed.. length must be exact 256..
>     // know of no other way to create a tuple with 256 elements...
>     var midiDataTuple = (z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z,
>  z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, 
> z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, 
> z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, 
> z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z,
>  z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z, z)
> 
>     
>     func midiSend(status: Int, val1: Int, val2 :Int)
>     {
>         var midipacket = MIDIPacket()
>         
>         midipacket.timeStamp = 0
>         midipacket.length    = 3
>         midipacket.data      = midiDataTuple  //<-=<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>         
>         midipacket.data.0 = UInt8(status)
>         midipacket.data.1 = UInt8(val1  )
>         midipacket.data.2 = UInt8(val2  )
>         
>         var midipacketlist = MIDIPacketList(numPackets: 1, packet: midipacket)
>         
>         MIDIReceived(midiSource, &midipacketlist)
>     }
>     
> I can't treat tuples as an array, which in this case would be handy to initialize all the tuple elements.
> 
> IfTrue: Why are tuples the only data type to use for unmanaged byte arrays? 
> 
> There's currently some work on a proposal for Contiguous Variables (A.K.A. Fixed Sized Array Type) <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160125/007984.html> which should help with the creation of tuples. (It can be read in a better fashion on gmane <http://thread.gmane.org/gmane.comp.lang.swift.evolution/4809>)
> 
> — Johan
>  

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