> On Jun 27, 2016, at 4:27 PM, Andrew Trick via swift-evolution > <[email protected]> wrote: > > >> On Jun 27, 2016, at 3:35 PM, Dave Abrahams <[email protected] >> <mailto:[email protected]>> wrote: >> >>> Casting from a raw pointer to a typed pointer is only more dangerous >>> than other raw pointer operations because it is the first step in this >>> sequence of operations, which is undefined: >>> >>> ptrA = rawPtr.cast(to: UnsafePointer<A>.self) >>> ptrA.initialize(with: A()) >>> ptrA.deinitialize() >>> >>> ptrB = rawPtr.cast(to: UnsafePointer<B>.self) >>> ptrB.initialize(with: B()) >> >> But it's trivial to get undefined behavior without any of that. Just: >> >> _ = rawPtr.load(UnsafePointer<NonTrivialType>.self) > > That's another way to obtain a typed pointer, but by itself it is well > defined. > > This is an important point, so I want to make sure I’m getting it across. > > The following code is well-defined: > ``` > ptrA = rawPtr.initialize(with: A()) > ptrA.deinitialize() > ptrB = rawPtr.initialize(with: B()) > ```
And updated for the proposal's current syntax... This is well-defined: ``` ptrA = rawPtr.initialize(A.self, with: A()) ptrA.deinitialize() ptrB = rawPtr.initialize(B.self, with: B()) ``` > The following code is undefined: > ``` > ptrA = rawPtr.cast(to: UnsafePointer<A>.self) > ptrA.initialize(with: A()) > ptrA.deinitialize() > ptrB = rawPtr.cast(to: UnsafePointer<B>.self) > ptrB.initialize(with: B()) > ``` > It is hard to spot the difference between the two styles without drawing > attention to the unsafe cast. > > I considered naming the cast `UnsafeRawPointer.bind<T>(to: T.Type)` to > indicate that the allocated memory is being bound to a type for the entire > duration of its allocation. But it's actually the call to `initialize` a > typed pointer that binds the type.
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