[swift-users] Passing Data to a f(void *) function

[Joe Groff]

> On Jun 30, 2017, at 7:40 AM, Martin R via swift-users <swift-users at 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:
> 
>    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 has been replaced by UnsafeRawPointer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.

This is a bug. The Data API ought to be using UnsafeRawPointer here.

-Joe