Hey folks.
I was not able to put that information in an update of wg21.link/P3867 in
the mailing, however there is an implementation on CE
https://compiler-explorer.com/z/qen1fvafq
The implementation (i.e a compiler builtin) is pretty small as it reuses
components that a compiler already necessarily have to implement
translation phase 6.

With my thanks to some folks at bloomberg who let me upstream that
prototype to their fork of clang.

Cheers,

On Tue, 13 May 2025 at 09:53, Corentin <corentin.jabot_at_[hidden]> wrote:

> Hey folks.
> STATICALLY-WIDEN <https://eel.is/c++draft/time.general#2> is a magic
> standard utility that conjures a string literal of a given type.
> This is implemented with macros.
>
> As we hopefully add char8_t support to format, we will want
> STATICALLY-WIDEN <https://eel.is/c++draft/time.general#2> to also support
> char8_t.
> At some point, this becomes cumbersome.
>
> We could envision that we have constexpr facilities to transcode to the
> literal encoding so that we could
> implement STATICALLY-WIDEN as
> define_static_string(to_literal_encoding(u8""));
>
> However, this might get fairly involved in terms of
> specification/implementation efforts (it boils down to making a constexpr
> interface over iconv)
>
> But it would be fairly easy for an implementation to support
> define_encoded_static_string<char>(u8""); as we already have the
> machinery in place to produce different sorts of string literals.
>
> Note that this gets more complicated if we want to accept something other
> than u8 as input, as it forces the compiler to be able to convert between
> arbitrary encoding, and requires more machinery than what is needed to
> implement [lex.string].
> The main use case for this is to convert string literals, so only
> supporting u8 inputs would not be limiting.
>
> Adapting the wording from P391,
> <https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3491r2.html>
> define_encoded_static_string could be specified as
>
> ---
> template <ranges::input_range R, *character-type* CharT>
> requires same_as<char8_t, ranges::range_value_t<R>>
> consteval const * define_encoded_static_string(R&& r);
>
> The sequence of characters denoted by the sequence of code units in r is
> encoded to a sequence of code units r' in the associated character encoding
> of the character type CharT. If a character lacks representation in the
> associated character encoding, or if r is not a valid UTF-8 code unit
> sequence, define_encoded_static_string is not a constant expression.
>
> Let V be the pack of elements of type CharT in r'. If r is a string
> literal, then V does not include the trailing null terminator of r.
> Let P be the template parameter object ([temp.param]) of type const
> CharT[sizeof...(V)+1] initialized with {V..., CharT()}.
> Returns: P.
> ----
>
> Was that considered?
> Cheers!
>
>
>