Ah, sneaky.  That code is fine because it uses unsafeCoerce# on "memcpy", changing memcpy from whatever type it is, into

MutableByteArray# s# -> MutableByteArray# s# -> Int# -> s# -> (# s#, () #)

 

So as long as the GC understands MutableByteArray# it's safe; it's relying on the C calling convention being handled properly.
 

On 8/21/07, Bulat Ziganshin <bulat.ziganshin@gmail.com> wrote:

Hello Stefan,

Tuesday, August 21, 2007, 10:08:59 AM, you wrote:

> Your code is broken in a most evil and insidious way.

and this code, too? :)

freezeSTUArray :: Ix i => STUArray s i e -> ST s (UArray i e)
freezeSTUArray (STUArray l u marr#) = ST $ \s1# ->
   case sizeofMutableByteArray# marr#  of { n# ->
   case newByteArray# n# s1#           of { (# s2#, marr'# #) ->
   case unsafeCoerce# memcpy marr'# marr# n# s2# of { (# s3#, () #) ->
   case unsafeFreezeByteArray# marr'# s3# of { (# s4#, arr# #) ->
   (# s4#, UArray l u arr# #) }}}}

> Unreproducable bugs are rarely reported, but they do add to people's
> impression of how unstable a language/library is.




--
Best regards,
Bulat                            mailto:Bulat.Ziganshin@gmail.com