> On Sep 19, 2016, at 1:24 AM, Martin R via swift-dev <swift-...@swift.org>
> wrote:
>
> I noticed that both UnsafePointer and UnsafeMutablePointer have the identical
> method
>
> public func withMemoryRebound<T, Result>(to: T.Type, capacity count: Int,
> _ body: (UnsafeMutablePointer<T>) throws -> Result) rethrows -> Result
>
> so that rebinding an immutable pointer gives you a _mutable_ pointer. That is
> different from what
>
> Unsafe[Mutable]Pointer<Pointee> {
> func withMemoryRebound<T>(to: T.Type, capacity count: Int,
> _ body: (Unsafe[Mutable]Pointer<T>) throws -> ()) rethrows
> }
>
> in
> https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md
> indicates. Perhaps I am misunderstanding something. Shouldn't rebinding an
> UnsafePointer result in an UnsafePointer again?
>
> Martin
I think you’re right about that. I didn’t notice the discrepancy until source
breaking changes were frozen and was concerned that fixing it would be more
restrictive.
Some users may migrate their code to:
constPtr.withMemoryRebound(to: T.self, capacity: 1) {
takesMutablePointer($0)
}
We probably want them to be more explicit:
constPtr.withMemoryRebound(to: T.self, capacity: 1) {
takesMutablePointer(UnsafeMutablePointer(mutating: $0))
}
We could possibly justify correcting this in Swift 3 though on these grounds:
- It’s effectively a bug considering that the proposal and implementation are
inconsistent.
- There is a correct way write the code that will continue to work before and
after fixing the bug.
- A simple fixit will tell them to add the “mutating” label.
If not, it’s something I was already planning to roll into Swift 4.
-Andy
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