#5218: Add unpackCStringLen# to create Strings from string literals -------------------------------------+------------------------------------- Reporter: tibbe | Owner: thoughtpolice Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.0.3 Resolution: | Keywords: strings Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #5877 #10064 | Differential Rev(s): Phab:D2443 #11312, #9719 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari):

I believe that one goal is

...

The ability to put a block of binary data in the program code, without heavy encoding.

Is that a goal? Can we focus solely on that for a while?

That is indeed a goal. Another in my mind equally-important goal is to be able to support constant-time length given the literals we write today. This is important for being able to efficiently implement things like `bytestring` `Builder` in terms of `memcpy`.

Or `B#` could be `ByteArray#`. That would have the major advantage of not adding a new type, and for sure we'd need to be able to turn it into a `ByteArray#`. So I like that, and it's what jscholl suggests in comment:74.

One issue with this is that we would gain a word of overhead for each string literal (assuming we use `B#` to implement Haskell's `String`). I took some measurements a while back and found that short strings are quite common, so this may be a hard cost to accept.

I don't have clarity on how bytestring would want to convert a `ByteArray#` to a `ByteString`. That ought to be a constant time operation.

I may be missing something but I don't believe this should pose any particular trouble. Afterall, a `ByteString` is essentially a `ForeignPtr` and some length/offset information. `byteArrayContents#` allows us to get the `Addr#` from a (pinned) `ByteArray#`, from which we can construct a `Ptr` and in turn a `ForeignPtr`. Since we are talking about static data `byteArrayContents#` should be safe. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5218#comment:91 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler