On 30 November 2004 09:35, John Meacham wrote:
On Tue, Nov 30, 2004 at 12:41:04AM -0800, Krasimir Angelov wrote:
Hello guys,
I am working on updated version of HDirect and now I am going to use CWString API to marshal (wchar_t *) type to String. I found some inconsistencies in the API. - castCWcharToChar and castCharToCWchar functions are defined only for Posix systems and they aren't exported. In the same time castCCharToChar and castCharToCChar have the same meaning and they are defined and exported on all platforms.
The problem is that these operations are very unsafe, there is no guarenteed isomorphism or even injection between wchar_ts and Chars. If people really know what they are doing, they can do the conversion themselves via fromIntegral/ord/chr, but I don't think we should encourage such unsafe usage with functions when it is simple for the user to work around it themselves.
That's right - castCWcharToChar and its dual are unlikely to be correct on Windows, where wchar_t is UTF-16. However, AFAICS the whole Windows API works in terms of UTF-16, only dealing with surrogate pairs in the text output routines. So it might sometimes be more convenient and efficient, but not strictly speaking correct, to do no conversion between a UTF-16 value and Haskell's Char in the FFI on Windows. I think we want to provide an interface that lets you do this if you know what you're doing. Cheers, Simon