expose strlen from Foreign.C.String

[Zemyla]

That doesn't sound right. I don't think it allocates any data on the heap
which could cause reallocation and move an unpinned ByteArray#, which is
the only way I can think it would be unsafe.

On Thu, Jan 21, 2021, 17:50 Andrew Martin <andrew.thaddeus at gmail.com> wrote:

> Both the unboxed variant and the wrapper are only sound on primitive
> string literals. You cannot use them on anything that was allocated at
> runtime, only on stuff baked into the rodata section. This is a pretty
> onerous restriction. What use case did you have in mind?
>
> Sent from my iPhone
>
> > On Jan 20, 2021, at 11:02 PM, Viktor Dukhovni <ietf-dane at dukhovni.org>
> wrote:
> >
> > 
> >>
> >>> On Jan 21, 2021, at 1:39 AM, chessai <chessai1996 at gmail.com> wrote:
> >>> On Wed, Jan 20, 2021, 17:01 Viktor Dukhovni <ietf-dane at dukhovni.org>
> wrote:
> >>>> On Wed, Jan 20, 2021 at 09:54:30AM -0800, chessai wrote:
> >>>>
> >>>> I've wanted the following before:
> >>>>
> >>>> foreign import ccall unsafe "strlen"
> >>>>   cstringLength# :: Addr# -> Int#
> >>>>
> >>>> cstringLength :: CString -> Int
> >>>> cstringLength (Ptr s) = I# (cstringLength# s)
> >>>>
> >>>> A natural place for this seems to be Foreign.C.String.
> >>>
> >>> Why a new FFI call, rather than `cstringLength#` from ghc-prim:
> GHC.CString
> >>> (as of GHC 9.0.1):
> >>
> >> I forgot about that addition. In that case we would just need the
> lifted wrapper
> >
> > No worries, sure the lifted wrapper makes sense, and Foreign.C.String
> does
> > look like a reasonable place in which to define, and from which to
> export it.
> >
> > --
> >    Viktor.
> >
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