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<regex>: Constants in std::regex_constants are not constexpr variables #4100
Description
Activity
Did you have an actual problem with a program you wrote, or is this just a paper bug report? I think it's better that these constants are prvalues - they don't waste space in object files. We should consider submitting an LWG issue to allow our implementation. (I suspect C++11 used constexpr variables out of an abundance of enthusiasm for the new feature, and not for any technical reason.)
Reacted by A. Jiang and Jonathan WakelyI think it's better that these constants are prvalues - they don't waste space in object files.
Oh, WG21-P0439R0 may be related - it changed previous enumerators to
constexprvariables. But in C++20 there'susing enum, so it's possible to keep the constants instdbeing prvalues while makingstd::memory_orderscoped.We talked about this at the weekly maintainer meeting and we're basically in agreement that this is legitimately a conformance issue, albeit one of extremely limited importance, and we would accept a PR to resolve this.
LWG-3998 is opened for this. Perhaps we can add "decision needed" back?
Describe the bug
The Standard specified that constants in
std::regex_constantsto beconstexprvariables ([re.const]).However, MSVC STL just implements them as enumerators of unscoped enumerations, which are not variables.
It seems that they have never been specified be to non-object. In TR1 (WG21-N1836) they were
static constvariables.Command-line test case
Godbolt link
Additional context
libc++ is similarly buggy (llvm/llvm-project#69420).
Also tracked by VSO-498998 / AB#498998 .