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[BUG]: error: lvalue required as increment operand #4100
Description
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Problem description
previously compiling code fails with gcc 12.1.0:
/usr/include/pybind11/pybind11.h:2347:29: error: lvalue required as increment operandrelevant code:
pybind11/include/pybind11/pybind11.h
Lines 2336 to 2360 in 1e3400b
Reproducible example code
#include <pybind11/pybind11.h>
#include <vector>
#include <pybind11/stl.h>
namespace py = pybind11;
using namespace py::literals;
class Vec {
public:
Vec(double x, double y, double z) {
values[0] = x;
values[1] = y;
values[2] = z;
};
double values[3];
};
PYBIND11_MODULE(mymodule, m) {
py::class_<Vec>(m, "Vec")
.def(py::init<double, double, double>())
.def("__iter__", [](const Vec& v){
return py::make_iterator(v.values, v.values+3);
}, py::keep_alive<0, 1>());
}
Activity
Skylion007 commentedon Aug 1, 2022
@hiaselhans Does this code snippit work with pybind11 2.9?
Simon-Lopez commentedon Oct 6, 2022
Hello,
Don't know if it helps but the code above compiles fine replacing:
with:
return py::make_iterator(v.values);(wich will then look for begin and end of v.values which is of type
const double[3]) or casting to raw pointer type with:or:
to select th right overloaded function.
Simon-Lopez commentedon Oct 6, 2022
It seems that the introduction of forwarding reference in 2.10.0 for:
iterator make_iterator(Iterator &&first, Sentinel &&last, Extra &&...extra)tends to favor the selection of:
iterator make_iterator(Type &value, Extra &&...extra)which leads to the "bug" above.
Simon-Lopez commentedon Oct 7, 2022
Could #4105 be related to this ?
(as the signature of py::make_iterator is changed ?)
Skylion007 commentedon Oct 7, 2022
@rwgk @henryiii reverting the perfect forwarding looks like a safe change as First and List is always an l-value in the C++ STL. @henryiii This seems to be similar the bug you have found in one of your projects when upgrading to 2.10?
henryiii commentedon Oct 7, 2022
Not me, but the regressions others found I listed in #4125. The regression for me has been the scikit_build_example one, which I need to work out before a release. The overload one is likely similar.
rwgk commentedon Oct 7, 2022
I think it's almost certainly a different kind of breakage.
The first major difference is compilation error vs runtime error.
rwgk commentedon Oct 7, 2022
This one? https://github.com/pybind/pybind11/pull/3860/files
Sounds good to me: I'm unable to foresee the side-effects one way or another (so many details come into play), but the older version is time-tested. Including something like the test in the PR description here with the rollback seems important.
Simon-Lopez commentedon Oct 10, 2022
I was just asking because I had runtime errors due to this very change. I did not investigate much further. :-/