Compile error: "error: invalid initialization of reference of type ‘std::move_iterator<const long unsigned int*>::reference {aka long unsigned int&&}’ from expression of type ‘std::remove_reference<const long unsigned int&>::type {aka const long unsigned int}’"

[bryanherger]

I attempted to compile current master (as of 05 Jul 2021) on CentOS 7.9.2009 with CMake 3.17.5 and g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44), but I get the following issue. Is a minimum g++ version required? v4.8.5 seems a bit dated relative to my OS release.

[ 66%] Building CXX object theta/test/CMakeFiles/theta_test.dir/theta_a_not_b_test.cpp.o
In file included from /usr/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/include/c++/4.8.2/string:40,
from /home/bryan/github/datasketches-cpp/common/test/catch.hpp:468,
from /home/bryan/github/datasketches-cpp/theta/test/theta_a_not_b_test.cpp:20:
/usr/include/c++/4.8.2/bits/stl_iterator.h: In instantiation of ‘std::move_iterator<_Iterator>::value_type&& std::move_iterator<_Iterator>::operator*() const [with _Iterator = const long unsigned int*; std::move_iterator<_Iterator>::reference = long unsigned int&&; std::move_iterator<_Iterator>::value_type = long unsigned int]’:
/usr/include/c++/4.8.2/bits/stl_algo.h:962:13: required from ‘_OIter std::copy_if(_IIter, _IIter, _OIter, _Predicate) [with _IIter = std::move_iterator<const long unsigned int*>; _OIter = std::back_insert_iterator<std::vector<long unsigned int, std::allocator > >; _Predicate = datasketches::key_less_than<long unsigned int, long unsigned int, datasketches::trivial_extract_key>]’
/home/bryan/github/datasketches-cpp/theta/include/theta_set_difference_base_impl.hpp:49:47: required from ‘CS datasketches::theta_set_difference_base<Entry, ExtractKey, CompactSketch, Allocator>::compute(FwdSketch&&, const Sketch&, bool) const [with FwdSketch = const datasketches::wrapped_compact_theta_sketch_alloc<std::allocator >; Sketch = datasketches::wrapped_compact_theta_sketch_alloc<std::allocator >; Entry = long unsigned int; ExtractKey = datasketches::trivial_extract_key; CompactSketch = datasketches::compact_theta_sketch_alloc<std::allocator >; Allocator = std::allocator]’
/home/bryan/github/datasketches-cpp/theta/include/theta_a_not_b_impl.hpp:37:63: required from ‘datasketches::theta_a_not_b_alloc::CompactSketch datasketches::theta_a_not_b_alloc::compute(FwdSketch&&, const Sketch&, bool) const [with FwdSketch = const datasketches::wrapped_compact_theta_sketch_alloc<std::allocator >; Sketch = datasketches::wrapped_compact_theta_sketch_alloc<std::allocator >; Allocator = std::allocator; datasketches::theta_a_not_b_alloc::CompactSketch = datasketches::compact_theta_sketch_alloc<std::allocator >]’
/home/bryan/github/datasketches-cpp/theta/test/theta_a_not_b_test.cpp:186:3: required from here
/usr/include/c++/4.8.2/bits/stl_iterator.h:963:37: error: invalid initialization of reference of type ‘std::move_iterator<const long unsigned int*>::reference {aka long unsigned int&&}’ from expression of type ‘std::remove_reference<const long unsigned int&>::type {aka const long unsigned int}’
{ return std::move(*_M_current); }
^
make[2]: *** [theta/test/CMakeFiles/theta_test.dir/theta_a_not_b_test.cpp.o] Error 1
make[1]: *** [theta/test/CMakeFiles/theta_test.dir/all] Error 2
make: *** [all] Error 2

[jmalkin]

Thanks for reporting this, I don't think anyone has tried it on 4.8.5 for a while. And I don't recall seeing it as an option in github actions, so we can't get it into our CI build. Operating on the idea that "untested == broken" I guess we should have expected this!

No ETA on this yet, but with luck we'll be able to look into it soon -- although there's a change the answer ends up being that we add a minimum gcc version.

[bryanherger]

I updated to devtools-7 with g++ (GCC) 7.3.1 20180303 (Red Hat 7.3.1-5) but still get an error. This would suggest it's somewhere else in my build environment - most likely libc/glibc since it's in an allocator, but would like to check or upgrade the full stack if needed. Can you let me know what release/version of components are used for CI?

EDIT: I deployed an AWS instance with latest Amazon Linux 2.0, installed build tools cmake3, gcc-c++, and git, and compiled without issue. So it might be useful to know what the CI environment is also, but clearly it's a version issue on my side.

[AlexanderSaydakov]

It seems to me that the problem has to do with a recently introduced wrapped_compact_theta_sketch. I would think that if you are not using this particular class in your code, it should continue to compile and work. If you would like to compile all unit tests, I would suggest commenting out the offending test in theta_a_not_b_test.cpp lines 170-190 for now.