expose strlen from Foreign.C.String

[Andrew Martin]

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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