> On 30. Jun 2017, at 16:57, Daniel Dunbar <daniel_dun...@apple.com> wrote:
>
>>
>> On Jun 30, 2017, at 7:40 AM, Martin R via swift-users
>> <swift-users@swift.org> wrote:
>>
>> I have a C function
>>
>> void myfunc(const void *ptr);
>>
>> which is imported to Swift as
>>
>> func myfunc(_ ptr: UnsafeRawPointer!)
>>
>> This compiles and runs without problems:
>>
>> let data = Data(bytes: [1, 2, 3, 4])
>> data.withUnsafeBytes { (ptr) in myfunc(ptr) } // (A)
>>
>> and the type of `ptr` is inferred as `UnsafePointer<Void>`. But adding an
>> explicit type
>> annotation produces a compiler warning:
>
> How do you know the inferred type is `UnsafePointer<Void>`? I think it is
> more likely it is `UnsafePointer<UInt8>`, and the following compiles:
> ```
> let data = Data(bytes: [1, 2, 3, 4])
> data.withUnsafeBytes { (ptr: UnsafePointer<UInt8>) in
> myfunc(ptr)
> }
> ```
>
> - Daniel
Command-click on "ptr" in "myfunc(ptr)" (or the Quick Help inspector) shows
let ptr: (UnsafePointer<()>)
>
>>
>> data.withUnsafeBytes { (ptr: UnsafePointer<Void>) in myfunc(ptr) } // (B)
>> // warning: UnsafePointer<Void> has been replaced by UnsafeRawPointer
>>
>> which is understandable in the view of "SE-0107 UnsafeRawPointer API".
>>
>> The "Fix-it" replaces `UnsafePointer<Void>` by `UnsafeRawPointer`, and that
>> does not
>> compile anymore:
>>
>> data.withUnsafeBytes { (ptr: UnsafeRawPointer) in myfunc(ptr) } // (C)
>> // error: cannot convert value of type 'Void' to closure result type '_'
>>
>> because there is no `withUnsafeBytes()` method taking a
>> `(UnsafeRawPointer)->ResultType`
>> closure.
>>
>>
>> My questions are:
>>
>> 1. Why are (A) and (B) treated differently?
>>
>> 2. Is (A) "legal", or should one use some non-void pointer
>>
>> data.withUnsafeBytes { (ptr: UnsafePointer<Int8>) in myfunc(ptr) } // (D)
>>
>> (which feels wrong to me because it is converted back to a void pointer when
>> calling the function).
>>
>> 3. Or should there be a `withUnsafeRawPointer()` method which makes (C)
>> compile as
>>
>> data.withUnsafeRawBytes { (ptr: UnsafeRawPointer) in myfunc(ptr) }
>>
>> This would also allow to access the data at byte offsets more easily, e.g.
>>
>> data.withUnsafeRawBytes { ptr in
>> let u16 = ptr.load(fromByteOffset: 4, as: UInt16.self)
>> }
>>
>> Does that makes sense?
>>
>> Regards, Martin
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>> swift-users mailing list
>> swift-users@swift.org
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