timd:
dons@cse.unsw.edu.au wrote:
The functions should document this behaviour better. Of course, you're paying with poke and C strings so you should be careful anyway. I'll correct the documentation to explain all this.
Forgive a non-experts comment:
This approach ("read the doco and be careful when you use these functions") feels contrary to the haskell ethos of pure code being reliably pure. What's the argument for not prefixing such functions with "unsafe"?
No no. The types should certainly reflect the safety. And by default people should try the safe versions :) Its a tricy area to get exactly right, since we're straddling the C / Haskell interface here. * The current api: Zero-copying, efficient. Unsafe if you mutate the C string, in the case of packMallocCString, if you run the finalisers twice: packCString :: CString -> ByteString packCStringLen :: CStringLen -> ByteString packMallocCString :: CString -> ByteString useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a Safe. Copies the ByteString: copyCString :: CString -> IO ByteString copyCStringLen :: CStringLen -> IO ByteString useAsCString :: ByteString -> (CString -> IO a) -> IO a * The proposed api: The following will be safe, copying across the C/Haskell boundary by default: packCString :: CString -> IO ByteString packCStringLen :: CStringLen -> IO ByteString packMallocCString :: CString -> IO ByteString useAsCString :: ByteString -> (CString -> IO a) -> IO a useAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a Those with extra efficiency needs, but also extra safety requirements: unsafePackCString :: CString -> IO ByteString unsafePackCStringLen :: CStringLen -> IO ByteString unsafePackMallocCString :: CString -> IO ByteString unsafeUseAsCString :: ByteString -> (CString -> IO a) -> IO a unsafeUseAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a Which will all do zero-copying calls acroos into C (or Haskell), but you'll need to ensure you don't mutate the C string. The safety requirements for the unsafe* versions will be clearly stated. -- Don