Is it possible to get from Any type his UnsafeRawPointer and length?

Using Swift
1

I just want call C function

static  inline  uint64_t  wyhash(const void* key,  uint64_t  len, uint64_t  seed)

from Swift like that

func hash<T: Any>(key: T, seed: UInt64) -> UInt64 { wyhash(...) }

Is it possible?

2

Not directly. If you can make your types conform to a protocol, though, then you can use a protocol extension method, because the Self type inside the extension will be the concrete conforming type:

protocol WyHashable { }

extension WyHashable {
  func hash(seed: UInt64) -> UInt64 {
    withUnsafeBytes(of: self) {
      return wyhash($0.startAddress!, UInt64($0.count), seed)
    }
  }
}
3

Is the size calculated correctly in this case?

protocol WyHashable { }

extension WyHashable {
  
  func hash(seed: UInt64) -> UInt64 {
    withUnsafeBytes(of: self) {
      print($0.count) // 8
      return wyhash($0.startAddress!, UInt64($0.count), seed)
    }
  }
}

extension Array: WyHashable where Element == Int { }

var arr = [21, 21, 21]
arr.hash(seed: ...)

Why the size in this case equals 8? Shouldn't it be 3 *8 ?

4

The problem with Array is that withUnsafeBytes is going to give you only the value representation, which is a pointer to the actual buffer. You might need to make the protocol have different behavior for different types if you want to be able to automatically handle arrays:

protocol WyHashable {
  func wyHash(seed: UInt64) -> UInt64 {
}

extension WyHashable {
  // Default implementation for trivial types, just hash the
  // value representation
  func wyHash(seed: UInt64) -> UInt64 {
    withUnsafeBytes(of: self) {
      return wyhash($0.startAddress!, UInt64($0.count), seed)
    }
  }
}

// Hash an array by its buffer contents
extension Array: WyHashable {
  func wyHash(seed: UInt64) -> UInt64 {
    self.withUnsafeBytes {
      return wyhash($0.startAddress!, UInt64($0.count), seed)
    }
  }
}
1 Like
5

It's all clear to me now. Thanks!

1 Like