dpiparo
commented
4 months ago I guess something wrong happens when one calls std::chrono::floor by basename (i.e. without namespace prefix). The statement above ends up with using of 'using namespace' with consequent calling of the bare floor template (without prefix).
Well, let's reproduce it by ourselves:
#include "Vc/vector.h"
#include <chrono>
void foo() {
std::chrono::nanoseconds dur;
std::chrono::floor<std::chrono::seconds>(dur);
}
$ c++ $(root-config --cflags) -std=c++17 -c a.cpp
$ Look, floor for std::chrono::duration works, unlike the example in the original message. Now let's rewrite it a bit:
#include "Vc/vector.h"
#include <chrono>
void foo() {
using namespace std::chrono;
nanoseconds dur;
floor<seconds>(dur);
}
$ c++ $(root-config --cflags) -std=c++17 -c a.cpp
In file included from a.cpp:1:
In file included from /Users/telzhov/opt/root/include/Vc/vector.h:32:
/Users/telzhov/opt/root/include/Vc/scalar/../common/../sse/../scalar/vector.h:50:5: error: static_assert failed due to requirement 'std::is_arithmetic<std::chrono::duration<long long, std::ratio<1, 1>>>::value' "Vector<T> only accepts arithmetic builtin types as template parameter T."
static_assert(std::is_arithmetic<T>::value,
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cpp:8:20: note: in instantiation of template class 'Vc_1::Vector<std::chrono::duration<long long>, Vc_1::VectorAbi::Scalar>' requested here
floor<seconds>(dur);
^
a.cpp:8:5: note: while substituting deduced template arguments into function template 'floor' [with T = std::chrono::duration<long long>]
floor<seconds>(dur);
^
1 error generated.In fact, floor for time_point is just a tiny wrapper for floor for duration, which calls bare floor, and that's where compilation fails:
#if _LIBCPP_STD_VER > 14
template <class _ToDuration, class _Clock, class _Duration>
typename enable_if
<
__is_duration<_ToDuration>::value,
time_point<_Clock, _ToDuration>
>::type
floor(const time_point<_Clock, _Duration>& __t)
{
return time_point<_Clock, _ToDuration>{floor<_ToDuration>(__t.time_since_epoch())};
// ^^^^^ here is a compiler error
}
I tried to insert std::chrono there (right to the 'chrono' header), and the code from my first message
void foo() {
std::chrono::time_point<std::chrono::system_clock,
std::chrono::nanoseconds> tp;
std::chrono::floor<std::chrono::seconds>(tp);
}got compiled.
mattkretz
Axel-Naumann
From the ROOT tracker ( this is a Vc issue) https://github.com/root-project/root/issues/11934 (Thanks to https://github.com/telzhov for the original report, copied here as it was!)
Describe the bug
ROOT Vc/vector.h and std::chrono both use at least four same names in their namespaces, i.e. floor, ceil, round, and abs. std:: and std::chrono:: are the different name spaces of course, but trying to instantiate an std::chrono::time_point doesn't compile if a compilation unit include's Vc/vector.h header as well (or any that includes it, such as Math/Minimizer.h etc).
Expected behavior
It should compile.
To Reproduce
Here is an example:
Trying to build
Try to comment out the line which includes Vc/vector.h, and you'll find that it works
Setup