Hi @qingfengxia , could you please paste the compilation error from your side? Thanks!

cancel_async exmple has error

template <typename F, typename... ArgsT> auto Executor::named_async(const std::string& name, F&& f, ArgsT&&... args)

Severity Code Description File Line Suppression State
Error C2672 'make_optional': no matching overloaded function found executor.hpp 871
Error C2660 'std::promise::set_value': function does not take 1 arguments executor.hpp 871
Error C2893 Failed to specialize function template 'std::optional<decay<_Ty>::type> std::make_optional(_Ty &&)' executor.hpp 847

I had some moderate trial (like make es5 code work in older browser), it does not work, it seems the compiler lack the feature to support make_optional()

Yes, I suspect it's an issue with MS compiler to detect the return value (type of the optional) that should be done correctly with auto-deduction. Could you please do the following change and report to me if the problem is still there?

// original code
else {
  p.object.set_value(cancel ? std::nullopt : std::make_optional(f(args...)));
}

// change to the following
else {
  if(cancel) {
    p.object.set_value(std::nullopt);
  }
  else {
    p.object.set_value(f(args...));
  }
}

// or you can do the following
else {
  std::optional<T> res;
  if(!cancel) {
    res = f(args...);
  }
  p.object.set_value(std::move(res));
 }

using your first solution, the std::opitonal error has gone, now get into second error message.

Severity Code Description File Line Suppression State
Error C2660 'std::promise::set_value': function does not take 1 arguments executor.hpp 876
Error C2661 'std::promise::set_value': no overloaded function takes 0 arguments executor.hpp 868

I think visual c++ 14.x, does not support if constexpr(std::is_same_v<R, void>) instead of that inside function body, would function template specialization help? with std::enable_if<>

==============================
There may be too many errors to solve

// Procedure: _on_pipe
template <typename... Ps>
void DataPipeline<Ps...>::_on_pipe(Pipeflow& pf, Runtime&) {
  }, _pipes, pf._pipe);

FAILED: examples/CMakeFiles/parallel_data_pipeline.dir/parallel_data_pipeline.cpp
Error C1004 unexpected end-of-file found data_pipeline.hpp 534

Do you have a C++17 compiler in your MSVC version? This might be the best way to get rid of constexpr error.

we have no chance to upgrade visual studio, I have solved the problem. named_async(), now the last error : unexpected end-of-file.

Reason: visual studio 2017 (16.35 latest) still does not support if-constexpr, inside lambda

broken parsing of greater-than comparison operator inside if-constexpr, inside lambda, inside std::visit

Solution from hints https://stackoverflow.com/questions/26421104/how-do-i-enable-if-a-class-with-variadic-template-arguments,

Here is my template function specialization for template ellipsis

// Function: named_async
template <typename F, typename... ArgsT>
auto Executor::named_async(const std::string& name, F&& f, ArgsT&&... args)
{
    return named_async_T<F, std::is_same_v<std::invoke_result_t<F, ArgsT...>, void>, ArgsT...>
        (name, std::forward<F>(f), std::forward<ArgsT>(args)...);
}


// add declaration
template <typename F, bool IsVoidRet, typename... ArgsT>
auto Executor::named_async_T(const std::string& name, F&& f, ArgsT&&... args)

// add impl, it is almost same as your original, but
           if constexpr (IsVoidRet) {
// instead of ,  it seems type_traits will fail in lambda.
           if constexpr (std::is_same_v<...> {

similarly problem and solution for: executor.hpp 26xx auto Subflow::_named_async

I can not make PR, so please fix this by change several lines.

Although I have not all examples compiled, but seems I have most features, so I can get started.
Thank you.

except for data_pipeline , all other example and unittest can be compiled.

@qingfengxia thanks! would you be willing to create a pull request? I guess you can skip the data pipeline compilation errors by not including its header in your application.

The newest version has removed this optional support in async task - should be no problem. Feel free to open another issue if the problem is still there.