C++ 20 Windows Build Problem

[TaeZStkyoht]

I am using your library. It could be built with C++ 17. But now I've changed my projects to be built with C++ 20 and it gives errors. Simple example error is like that:

int main() {
    vector<int> asd = { 3, 4, 1, -1, 565 };
    for (int b : from(asd).where([](int a) { return a > 3; }).toStdVector())
        cout << b << endl;

    return 0;
}

Severity    Code    Description Project File    Line    Suppression State
Error (active)  E0135   class "boolinq::Linq<std::tuple<boolinq::Linq<std::pair<std::_Vector_const_iterator<std::_Vector_val<std::conditional_t<true, std::_Simple_types<int>, std::_Vec_iter_types<int, size_t, ptrdiff_t, int *, const int *, int &, const int &>>>>, std::_Vector_const_iterator<std::_Vector_val<std::conditional_t<true, std::_Simple_types<int>, std::_Vec_iter_types<int, size_t, ptrdiff_t, int *, const int *, int &, const int &>>>>>, int>, int>, int>" has no member "toStdVector"

[k06a]

@TaeZStkyoht seems really strange that class "boolinq::Linq<***>" has no member "toStdVector", because it has this method:

https://github.com/k06a/boolinq/blob/a362fe917a47a784e818c6b27de29833776eefbc/include/boolinq/boolinq.h#L600-L607

What compiler and version do you use?

[TaeZStkyoht]

I'm using Visual Studio 2019 v16.11.1 on Windows. By the way it's not only toStdVector but also almost all other functions.

[RoqueDeicide]

result_of is deprecated in c++ 20 and needs to be replaced with invoke_result.

[k06a]

@RoqueDeicide @TaeZStkyoht @ZumZoom any ideas how to write universal code using result_of in pre-C++17 and invoke_result_t in C++17+?

[RoqueDeicide]

This code, when put at the top of the file, should allow the rest of the code to stay the same:

#if (defined(_MSC_VER) && _MSVC_LANG >= 202002L) || __cplusplus >= 202002L

namespace std
{
    template<typename _Callable, typename ..._Args>
    using result_of = std::invoke_result<_Callable, _Args...>;
}

#endif

[TaeZStkyoht]

@k06a Are you planning apply these changes, making a new release and updating it on vcpkg?

[k06a]

@TaeZStkyoht applied changes to master branch and added tag 3.0.3. Checking ways to submit new version to vcpkg.

[TaeZStkyoht]

@k06a Ok, thanks a lot.

[Mrhyuan]

It seems the version on vcpkg and conan is still 3.0.2. Any plan to update? Thx.

[k06a]

@Mrhyuan requested cvpkg upgrade here: https://github.com/microsoft/vcpkg/issues/22173

[k06a]

@Mrhyuan done via https://github.com/microsoft/vcpkg/pull/22177

[Mrhyuan]

@Mrhyuan done via microsoft/vcpkg#22177

So fast thank you so much

[TaeZStkyoht]

@k06a Ok "toStdVector" works now but some of them still doesn't work (especially "select"). Did you try your examples on your readme page? They don't work. Now I'm using Visual Studio 2019 16.11.8, _MSC_VER 1929, _MSVC_LANG 202002L. Your defined macro (The result_of was deprecated since C++20, so redefine it using invoke_result) is active because these versions satisfy it.

Your example:

int src[] = { 1,2,3,4,5,6,7,8 };
    auto dst = from(src).where([](int a) { return a % 2 == 1; })      // 1,3,5,7
        .select([](int a) { return a * 2; })           // 2,6,10,14
        .where([](int a) { return a > 2 && a < 12; }) // 6,10
        .toStdVector();

Errors:

• 'boolinq::Linq<std::tuple<boolinq::Linq<std::tuple<boolinq::Linq<std::pair<const int ,const int >,int>,int>,T>,int>,_TRet> boolinq::Linq<std::tuple<boolinq::Linq<std::pair<const int ,const int >,T>,int>,T>::select(F) const': could not deduce template argument for '_TRet'
• 'boolinq::Linq<std::tuple<boolinq::Linq<std::pair<const int ,const int >,int>,int>,T>::select': no matching overloaded function found

It still works with C++17 on Windows and any modern C++ version on Linux.

@RoqueDeicide Did you also try your work?

[k06a]

@TaeZStkyoht try to specify lambda return type as int

[k06a]

Sad to hear that. This means our template to get return type is not working as expected.

[RoqueDeicide]

61 Should fix this for good.

[TaeZStkyoht]

@RoqueDeicide nope. It will not be copiled gcc trunk and clang trunk. @k06a use my suggestion. This is the only compatible solution for now. If you decide not to support before C++17 in the future, just remove this definition and use invoke_result instead. Here you can try on GodBolt: https://godbolt.org/z/GhfezTrnb

[TaeZStkyoht]

And lol @RoqueDeicide You just copied my code and created own pull request? You commited 29 mins ago:

I commited 5 hours ago:

[TaeZStkyoht]

And after 5 hours try, I found compatible solution:

[RoqueDeicide]

@TaeZStkyoht, My code is based on "possible implementation" section of result_of article on cppreference.com Please, refrain from baseless accusations.

I'm not sure about compatibility with compilers that hadn't removed result_of as that just makes them not compatible with c++20 standard.

[k06a]

@TaeZStkyoht @RoqueDeicide thanks for the contributions, I will merge both and resolve conflicts 😁👌👍

[k06a]

Merged both, introduced subnamespace priv to avoid collisions incase of using both std and boolinq namespaces!