On Tue, Mar 12, 2024 at 7:15 AM Sebastian Wittmeier via Std-Proposals <std-proposals@lists.isocpp.org> wrote:

To be fair:
How much different is it in power from a C23 #embed?
Both feature that certain files, the ones which the implementation allows, can be fully (binarily) read at compile time.
Differences:
- the filepath can be created at runtime -> better hiding of the file read read; C23 probably supports macros for the filepath?
- the contents can be processed by constexpr functions -> probably the same can be achieved by mixing C23 with C++ constexpr
- the files could be read several times -> Denial of Service build; a long build can probably be achieved by other ways

The big one is the the filepath can be created at "runtime." Yes, #embed allows you to use macros — for example you can now write a quine as https://godbolt.org/z/hTj8jvcf8

— but you can't actually smuggle in a fully constexpr-evaluated string like https://godbolt.org/z/v74GdjKse

constexpr char myfilename[] = "test.txt";
constexpr char data[] = {
#embed (myfilename) // doesn't work
};

So #embed doesn't seem to be useful as a "constexpr filesystem," unfortunately.

Similarly, AFAICT no vendor supports `_Pragma(mystring)` with mystring a constexpr-evaluated string; the argument must be literally a string literal. But IIUC, C++26 is getting `static_assert(false, mystring)` — not with char arrays, but at least with strings and string_views. Example: https://godbolt.org/z/vdjf9KP3E

my $.02,

–Arthur