Pitch: Replace UnsafeMutablePointer by UnsafePointer in non-mutating APIs

Evolution Pitches
1

# Replace `UnsafeMutablePointer` by `UnsafePointer` in non-mutating APIs

* Proposal: [SE-0000](0000-change_unsafe_mutable_pointer_to_unsafe_pointer.md)
* Author: [Arnold Schwaighofer](https://github.com/aschwaighofer\)
* Status: **Pitch**
* Review manager: TBD

## Introduction

`UnsafeMutablePointer` didn't always have an immutable variant, and when it was
introduced there could have been many places that should have been changed to
use it, but were not. `UnsafeMutablePointer` is still pervasive. We should
survey the uses and make sure they're all using mutability only as appropriate.

The only such occurrence I found was the `dprintf` API which should have a
read-only format argument.

- Swift bug: [SR-1958] (https://bugs.swift.org/browse/SR-1958\)
- Branch with changes to stdlib: [unsafe_mutable_pointer_to_unsafe_pointer] (https://github.com/aschwaighofer/swift/tree/unsafe_mutable_pointer_to_unsafe_pointer\)

## Motivation

We should change uses of `UnsafeMutablePointer` with `UnsafePointer` to clearly
express the intent of the API where appropriate.

## Proposed solution

The proposed solution is to change `dprintf` API to take a `UnsafePointer`
argument.

## Detailed design

Change:

public func dprintf(_ fd: Int, _ format: UnsafeMutablePointer<Int8>, _ args: CVarArg...) -> Int32

To

public func dprintf(_ fd: Int, _ format: UnsafePointer<Int8>, _ args: CVarArg...) -> Int32

## Impact on existing code

Existing coersions to `UnsafePointer` from `UnsafeMutablePointer` will allow
existing code to work.

## Alternatives considered

Leave as is.

2

# Replace `UnsafeMutablePointer` by `UnsafePointer` in non-mutating APIs

* Proposal: [SE-0000](0000-change_unsafe_mutable_pointer_to_unsafe_pointer.md)
* Author: [Arnold Schwaighofer](https://github.com/aschwaighofer\)
* Status: **Pitch**
* Review manager: TBD

## Introduction

`UnsafeMutablePointer` didn't always have an immutable variant, and when it was
introduced there could have been many places that should have been changed to
use it, but were not. `UnsafeMutablePointer` is still pervasive. We should
survey the uses and make sure they're all using mutability only as appropriate.

The only such occurrence I found was the `dprintf` API which should have a
read-only format argument.

In that case you don't really need to go through evolution for this.
dprintf is effectively an API imported from POSIX in an overlay. We
should just fix it.

···

on Tue Jul 19 2016, Arnold Schwaighofer <swift-evolution@swift.org> wrote:

- Swift bug: [SR-1958] (https://bugs.swift.org/browse/SR-1958\)
- Branch with changes to stdlib:
[unsafe_mutable_pointer_to_unsafe_pointer]
(https://github.com/aschwaighofer/swift/tree/unsafe_mutable_pointer_to_unsafe_pointer\)

## Motivation

We should change uses of `UnsafeMutablePointer` with `UnsafePointer` to clearly
express the intent of the API where appropriate.

## Proposed solution

The proposed solution is to change `dprintf` API to take a `UnsafePointer`
argument.

## Detailed design

Change:

public func dprintf(_ fd: Int, _ format: UnsafeMutablePointer<Int8>, _ args: CVarArg...) -> Int32

To

public func dprintf(_ fd: Int, _ format: UnsafePointer<Int8>, _ args: CVarArg...) -> Int32

## Impact on existing code

Existing coersions to `UnsafePointer` from `UnsafeMutablePointer` will allow
existing code to work.

## Alternatives considered

Leave as is.

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

--
Dave

3

Is this limited to auditing the stdlib only or other APIs as well with
Swift overlays/API notes?

···

On Tue, Jul 19, 2016 at 16:47 Arnold Schwaighofer via swift-evolution < swift-evolution@swift.org> wrote:

# Replace `UnsafeMutablePointer` by `UnsafePointer` in non-mutating APIs

* Proposal: [SE-0000](
0000-change_unsafe_mutable_pointer_to_unsafe_pointer.md)
* Author: [Arnold Schwaighofer](https://github.com/aschwaighofer\)
* Status: **Pitch**
* Review manager: TBD

## Introduction

`UnsafeMutablePointer` didn't always have an immutable variant, and when
it was
introduced there could have been many places that should have been changed
to
use it, but were not. `UnsafeMutablePointer` is still pervasive. We should
survey the uses and make sure they're all using mutability only as
appropriate.

The only such occurrence I found was the `dprintf` API which should have a
read-only format argument.

- Swift bug: [SR-1958] (https://bugs.swift.org/browse/SR-1958\)
- Branch with changes to stdlib:
[unsafe_mutable_pointer_to_unsafe_pointer] (
GitHub - aschwaighofer/swift at unsafe_mutable_pointer_to_unsafe_pointer
)

## Motivation

We should change uses of `UnsafeMutablePointer` with `UnsafePointer` to
clearly
express the intent of the API where appropriate.

## Proposed solution

The proposed solution is to change `dprintf` API to take a `UnsafePointer`
argument.

## Detailed design

Change:

public func dprintf(_ fd: Int, _ format: UnsafeMutablePointer<Int8>, _
args: CVarArg...) -> Int32

To

public func dprintf(_ fd: Int, _ format: UnsafePointer<Int8>, _ args:
CVarArg...) -> Int32

## Impact on existing code

Existing coersions to `UnsafePointer` from `UnsafeMutablePointer` will
allow
existing code to work.

## Alternatives considered

Leave as is.

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

4

I limited this to the stdlib.

···

On Jul 19, 2016, at 2:57 PM, Xiaodi Wu <xiaodi.wu@gmail.com> wrote:

Is this limited to auditing the stdlib only or other APIs as well with Swift overlays/API notes?
On Tue, Jul 19, 2016 at 16:47 Arnold Schwaighofer via swift-evolution <swift-evolution@swift.org> wrote:
# Replace `UnsafeMutablePointer` by `UnsafePointer` in non-mutating APIs

* Proposal: [SE-0000](0000-change_unsafe_mutable_pointer_to_unsafe_pointer.md)
* Author: [Arnold Schwaighofer](https://github.com/aschwaighofer\)
* Status: **Pitch**
* Review manager: TBD

## Introduction

`UnsafeMutablePointer` didn't always have an immutable variant, and when it was
introduced there could have been many places that should have been changed to
use it, but were not. `UnsafeMutablePointer` is still pervasive. We should
survey the uses and make sure they're all using mutability only as appropriate.

The only such occurrence I found was the `dprintf` API which should have a
read-only format argument.

- Swift bug: [SR-1958] (https://bugs.swift.org/browse/SR-1958\)
- Branch with changes to stdlib: [unsafe_mutable_pointer_to_unsafe_pointer] (https://github.com/aschwaighofer/swift/tree/unsafe_mutable_pointer_to_unsafe_pointer\)

## Motivation

We should change uses of `UnsafeMutablePointer` with `UnsafePointer` to clearly
express the intent of the API where appropriate.

## Proposed solution

The proposed solution is to change `dprintf` API to take a `UnsafePointer`
argument.

## Detailed design

Change:

public func dprintf(_ fd: Int, _ format: UnsafeMutablePointer<Int8>, _ args: CVarArg...) -> Int32

To

public func dprintf(_ fd: Int, _ format: UnsafePointer<Int8>, _ args: CVarArg...) -> Int32

## Impact on existing code

Existing coersions to `UnsafePointer` from `UnsafeMutablePointer` will allow
existing code to work.

## Alternatives considered

Leave as is.

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution