Switch to C++17

[denravonska]

This is more of a maybe-next-year kind of thing, but I propose we switch from C++11 to C++14 or even C++17 to be able to utilize new functionality and optimizations. Some things we would directly benefit from are:

string_view (C++17)

Allows you to view a part of a string instead of making a copy. Replaces many usages of substr which speeds up boincblock unpacking and ExtractXML.

• gcc-7
• clang-4

std::optional (C++17)

Replaces the need to manually carry an is-initialized flag, see StructCPID.

• gcc-7
• clang-4

std::filesystem (C++17)

Replaces boost::filesystem.

• gcc-8
• clang-7

Splicing for maps and sets

Cheaper data move between containers.

• gcc-7
• clang-8

std::variant (C++17)

Replaces boost::variant.

• gcc-7
• clang-4

Relaxing constraints on constexpr functions (C++14)

Allows more flexibility in constexpr functions which gives the compiler a better chance at optimizing.

• ??

STL constexpr improvements (C++14)

Several functions in the STL have been made constexpr.

• gcc-5
• clang-3.4

Parallel algorithms (C++14)

Allows for standard algorithm (find, sort etc) to utilize more cores.

• Not yet supported in gcc or clang

[jamescowens]

We will not be able to do this until Ubuntu 16.04 is EOL I think. C++14 is covered by GCC5+

[nathanielcwm]

Ubuntu EOL is April 2021 according to: https://wiki.ubuntu.com/Releases

https://gcc.gnu.org/projects/cxx-status.html#cxx17

[jamescowens]

Looks like GCC compiler version 7+ has all of the features. This is in 18.04+. So we have to wait until 16.04 is retired, although there are already some problems compiling on 16.04.

[div72]

@jamescowens Ubuntu 16.04 is EOL in 2.5 weeks(2021-04-30). Are we clear to bump by then or should we provide a little more time?

[jamescowens]

We probably should make an announcement about our intentions on Reddit first and hold for a while.

[jamescowens]

But I do not want to wait too long...