无法推断出通用参数“自我”

Question

I'm trying to convert bytes in values from a bluetooth device i'm using, but I'm getting Generic parameter 'Self' could not be inferred on this and I don't know what it means

var speed: UInt16 = 0
_ = withUnsafeBytes(of: &speed, {characteristic.value!.copyBytes(to: $0, from: 0...1)})

Answer 1

The error message is misleading. The actual problem is that withUnsafeBytes invokes the closure with a read-only buffer pointer to the raw bytes of the given argument. What you need is withUnsafeMutableBytes :

var speed: UInt16 = 0
_ = withUnsafeMutableBytes(of: &speed, {
    characteristic.value!.copyBytes(to: $0, from: 0...1)
})

Answer 2

needed to change to

_ = withUnsafeMutableBytes(of: &speed, {
    characteristic.value!.copyBytes(to: UnsafeMutuableBufferPointer(to: $0. count: 1), from: 0..<1)
})