Martin
(Martin R)
1
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 swift-evolution/0107-unsaferawpointer.md at master · apple/swift-evolution · GitHub 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
···
On Sep 19, 2016, at 1:24 AM, Martin R via swift-dev <swift-dev@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
You’re right. There is an inconsistency between the proposal and Swift 3 implementation. I’ve been thinking about whether it makes more sense to correct this sooner or later. I responded in more detail on swift-evolution.
-Andy
···
On Sep 19, 2016, at 1:24 AM, Martin R via swift-dev <swift-dev@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
dabrahams
(Dave Abrahams)
4
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.
It's definitely a bug, IMO.
···
on Mon Sep 19 2016, Andrew Trick <swift-evolution@swift.org> wrote:
On Sep 19, 2016, at 1:24 AM, Martin R via swift-dev <swift-dev@swift.org> wrote:
- 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
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
--
-Dave
If there’s no objection, I’ll just go ahead with a fix on the 3.0 branch since it was already covered by SE-0107.
-Andy
···
On Sep 19, 2016, at 11:44 PM, Dave Abrahams via swift-evolution <swift-evolution@swift.org> wrote:
on Mon Sep 19 2016, Andrew Trick <swift-evolution@swift.org> wrote:
On Sep 19, 2016, at 1:24 AM, Martin R via swift-dev <swift-dev@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.
It's definitely a bug, IMO.
- 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.
