[swift-evolution] [Review] SE-0055 Make unsafe pointer nullability explicit using Optional

Jordan Rose jordan_rose at apple.com
Mon Mar 28 13:46:29 CDT 2016

Thank you for elaborating on your concerns! Some responses below.

> On Mar 28, 2016, at 11:09, Антон Жилин <antonyzhilin at gmail.com> wrote:
> UnsafeBufferPointer is currently represented as a (nullable) C pointer plus size. It can be implemented almost in pure Swift (with calls to C functions).
> After the proposal is accepted, it will be replaced with Optional<UnsafeBufferPointer>.

That is not the proposal; please re-read the section on UnsafeBufferPointer. <https://github.com/apple/swift-evolution/blob/master/proposals/0055-optional-unsafe-pointers.md#unsafebufferpointer> (You might not be happy with this version either, though.)

> But it will require a compiler-only "hack" for Optional not to require extra memory for nil (I assume, Optional will look into address part of UnsafeBufferPointer). This symbiosis will have to be built in the compiler, and I call that "compiler magic".

This is actually standard behavior for all enum types (guaranteed) and all struct types whose first property is such an enum or built-in type with available "extra inhabitants" (an optimization whose details may change in the future). This includes structs beginning with a non-optional AnyObject, and enum types you define like this:

enum Maybe<T> {
  case just(T)
  case nothing

If 'T' is a type that has a known invalid representation, such as AnyObject, that representation will be used for the 'nothing' case of 'Maybe<T>'

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