[swift-users] Updating C-wrapper to Swift 3

[John Brownie]

Thanks for the pointers. Good reading, but I'm still confused. I think 
that the first issue is clear to me now, but I don't know what I have to 
do to make the closure be seen as satisfying the type of the function 
pointer. It worked in Swift 2.2 as

             XML_SetEndElementHandler(parser) { (userData: 
UnsafeMutablePointer<Void>, name: UnsafePointer<XML_Char>) -> Void in

All that's changed is making the UnsafeMutablePointer<Void> into 
UnsafeMutableRawPointer, unless it's the unwrapped nature of the 
parameter in the error message:

Cannot convert value of type '(UnsafeMutableRawPointer, 
UnsafePointer<XML_Char>) -> Void' to expected argument type 
'XML_EndElementHandler!'

I don't know what I need to do next. Any help is much appreciated.
> Quinn "The Eskimo!" via swift-users <mailto:swift-users at swift.org>
> 28 September 2016 at 11:26
>
> I recommend reading the whole “Migrating to Swift 2.3 or Swift 3 from 
> Swift 2.2” doc, but for this specific issue you should start with the 
> “UnsafeRawPointer Migration” doc that it links to.
>
> <https://swift.org/migration-guide/>
>
> <https://swift.org/migration-guide/se-0107-migrate.html>
>
> Share and Enjoy
> --
> Quinn "The Eskimo!" <http://www.apple.com/developer/>
> Apple Developer Relations, Developer Technical Support, Core OS/Hardware
>
>
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
> John Brownie <mailto:john_brownie at sil.org>
> 28 September 2016 at 9:29
> I have a Swift wrapper for the expat XML parser, and I just went 
> through the update to Swift 3, and I'm thrown a series of errors that 
> mostly appear to be of two types. Here is a representative function of 
> the first type:
>
>     func parse() throws {
>         var done = false
>         while !done {
>             let buffer: UnsafeMutablePointer<Void> = 
> XML_GetBuffer(parser, Int32(bufsize))
>             if buffer == nil {
>                 let errorCode = XML_GetErrorCode(parser)
>                 throw ExpatError(reason: "Error \(errorCode), 
> \(XML_ErrorString(errorCode))")
>             }
>             let bytesRead = 
> readData(UnsafeMutablePointer<UInt8>(buffer), bufferLength: bufsize)
>             done = bytesRead < bufsize
>             if XML_ParseBuffer(parser, Int32(bytesRead), Int32(done ? 
> 1 : 0)) != XML_STATUS_OK {
>                 let errorCode = XML_GetErrorCode(parser)
>                 throw ExpatError(reason: "Error \(errorCode), 
> \(XML_ErrorString(errorCode))")
>             }
>         }
>     }
>
> Xcode 8's migrator changed the declaration of buffer to 
> UnsafeMutableRawPointer?, but the readData call gives an error:
>
> Cannot invoke initializer for type 'UnsafeMutablePointer<UInt8>' with 
> an argument list of type '(UnsafeMutableRawPointer?)'
> Pointer conversion restricted: use '.assumingMemoryBound(to:)' or 
> '.bindMemory(to:capacity:)' to view memory as a type.
> Overloads for 'UnsafeMutablePointer<UInt8>' exist with these partially 
> matching parameter lists: (RawPointer), (OpaquePointer), 
> (OpaquePointer?), (UnsafeMutablePointer<Pointee>), 
> (UnsafeMutablePointer<Pointee>?)
>
> Where can I read up on how to make the conversion? My initial effort is:
>
>             let bytesRead = readData(buffer!.bindMemory(to: 
> UInt8.self, capacity: bufsize), bufferLength: bufsize)
>
> That's more or less thrashing around with no real understanding.
>
> The second type is turning a closure into the appropriate C function 
> pointer. For example:
>
>             XML_SetEndElementHandler(parser) { (userData: 
> UnsafeMutableRawPointer, name: UnsafePointer<XML_Char>) -> Void in
>                 let theParser = unsafeBitCast(userData, to: 
> ExpatSwift.self)
>                 let theName = ExpatSwift.getString(name)
>                 theParser.endElement(theName)
>             }
>
> This gets an error:
>
> Cannot convert value of type '(UnsafeMutableRawPointer, 
> UnsafePointer<XML_Char>) -> Void' to expected argument type 
> 'XML_EndElementHandler!'
>
> XML_EndElementHandler is defined as:
>
> typedef void (XMLCALL *XML_EndElementHandler) (void *userData,
>                                                const XML_Char *name);
>
> Here I have no real clue as to how to fix it.
>
> So, any pointers to either how to fix these problems or to a good 
> source to read to understand them?
>
> John

-- 
John Brownie
In Finland on furlough from SIL Papua New Guinea
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