swift-mirror/userdocs/diagnostics/unsafe.md

Unsafe code wanings (Unsafe)

This diagnostic group includes warnings that identify the use of unsafe language constructs and library APIs. Example warnings include:

• Use of an unsafe language feature:

  // warning: unowned(unsafe) involves unsafe code
  unowned(unsafe) var parentNode: TreeNode<T>
  

• Use of a function or type annotated with @unsafe:

  // warning: reference to unsafe generic struct 'UnsafeMutablePointer'
  func getPointee<T>(_ pointer: UnsafeMutablePointer<Int>, as type: T.Type) -> T {
    // warning: call to unsafe global function 'unsafeBitCast'
    return unsafeBitCast(pointer.pointee, to: type)
  }
  

• Use of a function involving an @unsafe type:

  func evilMalloc(size: Int) -> Int {
    // warning: call to global function 'malloc' involves unsafe type 'UnsafeMutableRawPointer'
    return Int(bitPattern: malloc(size))
  }
  

These warnings can be suppressed using an unsafe expression, which acknowledges the presence of memory-unsafe code. For example:

func evilMalloc(size: Int) -> Int {
  return unsafe Int(bitPattern: malloc(size))
}

The warnings produced by this diagnostic group can be enabled with the compiler flag -strict-memory-safety.