Compilation of examples failed on gcc 9, 10 and 11

[YuraCobain]

Expected Behavior

Compilation of examples by gcc 9,10,11 is successfuly

Actual Behavior

Compilation is failed by gcc 9.4.0, 10.3.0 and 11.1.0 with following errors:
Non-member CircleMember Square[ 92%] Built target unified
[ 96%] Building CXX object test/CMakeFiles/te.dir/te.cpp.o
In file included from /home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/test/te.cpp:13:
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp: In instantiation of ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, std::index_sequence<Ns ...>) [with T = Square; T_ = Square; long unsigned int ...Ns = {}; I = DrawableT<std::basic_ostream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable; std::index_sequence<Ns ...> = std::integer_sequence]’:
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:463:68: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, TRequires) [with T = Square; T_ = Square; TRequires = boost::ext::te::v1::detail::type_list; I = DrawableT<std::basic_ostream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:443:74: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&) [with T = Square; T_ = Square; typename std::enable_if<(! is_same_v<T_, boost::ext::te::v1::poly<I, TStorage, TVtable> >), bool>::type = true; I = DrawableT<std::basic_ostream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/test/te.cpp:486:56: required from here
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:475:33: error: static assertion failed
475 | static_assert(sizeof...(Ns) > 0);
| ~~~~~~~~~~~~~~^~~
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp: In instantiation of ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, std::index_sequence<Ns ...>) [with T = Circle; T_ = Circle; long unsigned int ...Ns = {}; I = DrawableT<std::cxx11::basic_stringstream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable; std::index_sequence<Ns ...> = std::integer_sequence]’:
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:463:68: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, TRequires) [with T = Circle; T = Circle; TRequires = boost::ext::te::v1::detail::type_list; I = DrawableT<std::cxx11::basic_stringstream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:443:74: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&) [with T = Circle; T = Circle; typename std::enable_if<(! is_same_v<T, boost::ext::te::v1::poly<I, TStorage, TVtable> >), bool>::type = true; I = DrawableT<std::cxx11::basic_stringstream >; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/test/te.cpp:493:61: required from here
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:475:33: error: static assertion failed
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp: In instantiation of ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, std::index_sequence<Ns ...>) [with T = <lambda()>::<lambda(int)>; T = <lambda()>::<lambda(int)>; long unsigned int ...Ns = {}; I = Function<int(int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable; std::index_sequence<Ns ...> = std::integer_sequence]’:
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:463:68: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, TRequires) [with T = <lambda()>::<lambda(int)>; T = <lambda()>::<lambda(int)>; TRequires = boost::ext::te::v1::detail::type_list; I = Function<int(int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:443:74: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&) [with T = <lambda()>::<lambda(int)>; T = <lambda()>::<lambda(int)>; typename std::enable_if<(! is_same_v<T_, boost::ext::te::v1::poly<I, TStorage, TVtable> >), bool>::type = true; I = Function<int(int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/test/te.cpp:541:59: required from here
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:475:33: error: static assertion failed
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp: In instantiation of ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, std::index_sequence<Ns ...>) [with T = <lambda()>::<lambda(int, int)>; T_ = <lambda()>::<lambda(int, int)>; long unsigned int ...Ns = {}; I = Function<int(int, int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable; std::index_sequence<Ns ...> = std::integer_sequence]’:
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:463:68: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&, TRequires) [with T = <lambda()>::<lambda(int, int)>; T_ = <lambda()>::<lambda(int, int)>; TRequires = boost::ext::te::v1::detail::type_list; I = Function<int(int, int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:443:74: required from ‘constexpr boost::ext::te::v1::poly<I, TStorage, TVtable>::poly(T&&) [with T = <lambda()>::<lambda(int, int)>; T_ = <lambda()>::<lambda(int, int)>; typename std::enable_if<(! is_same_v<T_, boost::ext::te::v1::poly<I, TStorage, TVtable> >), bool>::type = true; I = Function<int(int, int)>; TStorage = boost::ext::te::v1::dynamic_storage; TVtable = boost::ext::te::v1::static_vtable]’
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/test/te.cpp:547:75: required from here
/home/ikobein/rnd/sw-engineering-rnd/boost-te-test/te/include/boost/te.hpp:475:33: error: static assertion failed
make[2]: *** [test/CMakeFiles/te.dir/build.make:76: test/CMakeFiles/te.dir/te.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:505: test/CMakeFiles/te.dir/all] Error 2
make: *** [Makefile:101: all] Error 2

Steps to Reproduce the Problem

Ubuntu 20.4, cmake 3.24.2, gcc 9.4.0, 10.3.0, 11.1.0
0.clone repository

1. mkdir build: cd build; cmake ..
2. make

[pfeatherstone]

This is a known issue and I'm pretty sure it's unfixable

[YuraCobain]

Thank you for reply.
Does it impact only this specific functionality covered in example and could turn off?
Is the rest of functionality stable on modern compilers?

[pfeatherstone]

This implementation is not guaranteed to work everywhere. It makes assumptions on the order things are compiled and analysed. By the time the compiler compiles poly, the implementation hopes the types are complete. The compiler might compile things in a different order in which case the types may not be complete by the time it gets to poly. In my opinion, you're better off taking the storages types and defining your erased types from scratch. It's not a lot of effort at all. The storage types do a lot of the heavy lifting and it will work!

[pfeatherstone]

We can provide some examples at some point

[pfeatherstone]

It's possible @krzysztof-jusiak will come up with some other implementation and make it work but it will no doubt require c++20 and likely a very modern compiler. That's not a bad thing. But using the storage types manually will work everywhere and even with c++14

[YuraCobain]

Thank you for detailed answer.
If you provide simple example with manual storage I appreciate it.

[pfeatherstone]

Sure. I can't do that now. But will try to remember tomorrow

[pfeatherstone]

https://godbolt.org/z/W3PxoKa1f
I recently submitted a PR to the dlib library which has storage policies. I put a bit more effort in that PR than i did in this one.

[pfeatherstone]

Yes it's a bit more manual but it works, compiles with C++14 and just as performant as libraries which implement polys, since performance bottlenecks will only ever be in the storage policies.

[YuraCobain]

Thanks a lot for demo.
So the same approach should work smoothly with std::any to not bring dlib dependency into scene, isn't it?
As I understand it's demo when project can't afford C++ higher than 14.

[pfeatherstone]

You can strip out the storage policies stuff from dlib. You should only need dlib/any/storage.h.

[pfeatherstone]

I imagine std::any uses a small buffer optimization (same as storage_sbo), or heap only (same as storage_heap). You don't get the others.

[pfeatherstone]

You can literally copy paste the contents of dlib/any/storage.h

[pfeatherstone]

But yeah you could do something similar with std::any. I like this because I can customize the SBO, create view types or shared types. It's quite flexible

[krzysztof-jusiak]

I've been working recently on a different project with similar approach and made it work with modern versions of gcc, clang, msvc. Will back port the solution to te but just wanted to let you know that it's possible.

[pfeatherstone]

Awesome ! Will it work with C++14?

[pfeatherstone]

https://godbolt.org/z/qe4dnM7T7 This one uses the storage policies in te instead of dlib.

[pfeatherstone]

I've been working recently on a different project with similar approach and made it work with modern versions of gcc, clang, msvc. Will back port the solution to te but just wanted to let you know that it's possible.

Do you have a timeline on when this will get merged. I'm super interested in this!