在Xcode 8（Swift 3）中，UnsafeMutablePointer <_>是什么意思？

Question

The following code:

  var mutableDataP = UnsafeMutablePointer<Int16>(audioBuffer.mData)
  let stereoSampleArray = UnsafeMutableBufferPointer(
      start: mutableDataP,
      count: nBytesInBuffer/sizeof(Int16)    // Int16 audio samples
  )

gives the following error:

Cannot convert value of type 'UnsafeMutablePointer' to expected argument type 'UnsafeMutablePointer<_>'

What is an UnsafeMutablePointer<__> and how do I cast to it? I tried all the casting variations I could think of and got un-understandable diagnostics for each and I've run out of ideas. I find the documentation on the various UnsafeMutablePointer types unhelpful, and no mention at all of '<_>'.

Answer 1

Try this change:

let stereoSampleArray = withUnsafeMutablePointer(to: &audioBuffer.mData){
       return UnsafeMutableBufferPointer(
              start: $0,
              count: nBytesInBuffer/MemoryLayout<Int16>.size    // Int16 audio samples
             )
       }

Where audioBuffer.mData is a var