Andrew Schwartzmeyer created MESOS-7142:
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Summary: Revisit MSVC decltype bug
Key: MESOS-7142
URL: https://issues.apache.org/jira/browse/MESOS-7142
Project: Mesos
Issue Type: Improvement
Components: libprocess
Environment: Windows with Visual Studio 2017 RC
Reporter: Andrew Schwartzmeyer
Assignee: Andrew Schwartzmeyer
Priority: Minor
Review https://reviews.apache.org/r/56781/ works around an existent and
acknowledged bug in MSVC. From MSVC team:
{quote}
I have preprocessed file from Andy yesterday, thank you. I can verify that this
is a bug in the latest compiler where it’s failing to get the right context for
the decltype expression for the return type of function. However, MSVC does
deduce the right type from the return expression in the body. We have a bug in
the compiler logged now and will be tracked for next release.
We’ll be adding Mesos project to our daily RealWorld Testing set from now on as
continuous validation for MSVC compiler. Thank you for bringing this up to our
attention.
template <typename F>
auto then(F&& f) const-> decltype(this->then(std::forward<F>(f), Prefer()))
Should really expand to this expression, but it’s failing.
template <typename F>
auto then(F&& f) const -> decltype(static_cast<const
Future<T>*>(this)->then(std::forward<F>(f), Prefer()))
The workaround from Michael to skip explicit return type for auto function
should be actually better source change for MSVC compiler. For completeness
sake, you can also just remove ‘this->’ from the decltype expression to make it
work for MSVC compiler
-> decltype(then(std::forward<F>(f), Prefer()))
Another thing worth pointing out is, adding ‘this->’ in the body of the
function shows that MSVC does correctly deduce the return type.
template <typename F>
auto then(F&& f) const
// -> decltype(then(std::forward<F>(f), Prefer()))
// -> decltype(static_cast<const
Future<T>*>(this)->then(std::forward<F>(f), Prefer()))
{
return this->then(std::forward<F>(f), Prefer());
}
{quote}
This issue tracks revisiting the work-around when the first patch to VS2017 is
released, as the compiler bug itself should be fixed then.
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