[squid-dev] RFC: Switch to C++17

[Francesco Chemolli]

I support the switch

On Sun, 4 Dec 2022 at 16:18, Alex Rousskov <rousskov at measurement-factory.com>
wrote:

> Hello,
>
>      I propose that we switch master/v6 from C++11 to C++17: Modern
> environments support C++17 well. We are wasting significant amounts of
> time on emulating such basic C++17 features as std::optional. We are
> writing worse code than we can because we lack access to such basic
> C++14 and C++17 features as
>
> * function return type deduction (auto)
> * generic lambdas (auto arguments)
> * relaxed constexpr restrictions
> * std::make_unique
> * std::integer_sequence
> * std::quoted
> * Nested namespace definitions
> * [[fallthrough]], [[maybe_unused]], and [[nodiscard]]
> * fold expressions
> * auto [a, b] = getTwoReturnValues();
> * inline variables
> * std::any
> * std::variant
> * std::byte
>
> If we do not switch now, then we would have to wait about a year for the
> next such opportunity because we should not introduce such a big
> difference between master and the upcoming unstable v6 branch.
>
>
> C++17 is supported by popular modern compilers and stable distros. Squid
> master branch should target those IMO. Even old environments can install
> the necessary modern compilers (e.g., RHEL5 users can get them via Red
> Hat Developer Toolset).
>
> * GCC v5 supports most C++17 features.
> * GCC v8 supports all relevant C++17 features.
> * Clang v5 supports nearly all C++17 features.
> * Clang v8 supports all relevant C++17 features.
>
> * Ubuntu 20.04 LTS ships with GCC v9 and clang v10.
>
> * https://gcc.gnu.org/projects/cxx-status.html#cxx17
> *
> https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2017
> * https://clang.llvm.org/cxx_status.html#cxx17
> * https://en.cppreference.com/w/cpp/compiler_support/17
>
>
> Switching to just C++14 would be better than nothing, but it will not
> give us several C++17 features that we already waste serious time on
> emulating/avoiding (e.g., std::optional). We should not switch to C++20
> yet because modern stable compilers still have some C++20 support holes.
>
>
> I can volunteer the corresponding PR.
>
>
> Any objections to switching master/v6 to C++17?
>
>
> Thank you,
>
> Alex.
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>
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