Hello Simon (et al.) While experimenting with refactoring/improving integer-gmp, I'd like to represent a GMP number just by a ByteArrays# (and thus save a redundant limb-count field). However, for that I'd need an efficient way to resize a MutableByteArray# for the result value in case its initial size over- (or under-)allocated. Right now I'd re-allocate via newByteArray# with the final size and copyMutableByteArray#, and now I was wondering if we couldn't simply have an unsafeShrinkMutableByteArray# :: MutableByteArray# s# -> Int# -> State# s -> State# s operation, which would allow for zero-copying. (the 'unsafe' denotes this wouldn't check if the new size is less-or-equal to the current size, and that one has to be careful when subsequently using sizeofMutableByteArray# which is currently a pure function) Is such an operation feasible, or is there something in the RTS/GC that would trip over when a ByteArray has suddenly a smaller byte-count than its originally newByteArray#'ed amount? PS: maybe unsafeShrinkMutableByteArray# could unsafe-freeze the ByteArray# while at it (thus be called something like unsafeShrinkAndFreezeMutableByteArray#), as once I know the final smaller size I would freeze it anyway right after shrinking. Cheers, hvr