Use C++17 language features

[salkinium]

We're already using C++14 by default, which requires at least GCC 5.
This is an issue for the official avr-gcc from Atmel which ships with Ubuntu in version 4.9.3.
Most other linux distributions, as well as macOS via Homebrew (Q: what about Windows?) compile their own avr-gcc from upstream, which is missing support for several AVR architectures and devices.
For the sake of moving forwards, we've accepted this caveat and are using a self-compiled avr-gcc 7.3.0 for our CI.
ARM already ships arm-none-eabi-gcc for v7.2.0 since the 2017q4 release.

The C++ standards support page for GCC shows that all language features of C++17 (except fixes to template argument deduction for class templates) are supported by GCC 7.
I would therefore like to enable C++17 as the default for modm to already make use of very useful new features such as constexpr if, enhancements to variadic templates, selection statements with initializers, constexpr lambdas and many more.

cc @dergraaf @strongly-typed @rleh @chris-durand @daniel-k @ekiwi @georgi-g @mhthies

[siy]

It was the thing which I was about to ask for.

[rleh]

arm-none-eabi-gcc

• ARM toolchain: GCC 7.1
  • PPA for Ubuntu 👍
  • Download (precompiled) for Windows 👍
  • Download (precompiled or source) for Linux 64-bit 👍
• Ubuntu (since bionic): GCC 6.3.1 👎 (but PPA see above)
• Debian: GCC 5.4.1 👎
• Fedora: GCC 7.1.0 with CodeSourcery patches 👍
• Arch Linux: GCC 8.1.0 👍
• macOS via Homebrew: GCC 7.2.0 👍
• Docker Container for CI: GCC 7.2.0 👍

avr-gcc

• Official Atmel toolchain 3.6.1: GCC 5.4 👎
• Debian: GCC 4.9.2 based on Atmel toolchain 3.5.3 👎
• Ubuntu (since Artful): GCC 5.4.0 based on Atmel toolchain 3.6.0 👎
• Fedora: GCC 7.2.0 👍
• Arch Linux: GCC 8.1.0 👍
• macOS via Homebrew: GCC 7.2.0 👍
• Docker Container for CI: GCC 7.3.0 👍
• Arduino ships with GCC 4.9.2 👎
• Somebody built GCC 8.1 for Windows in May 2017 👍

[salkinium]

If you use 32-bit Linux, well… meh.
I guess in the worst case you can always provide a Docker container for some precompiled avr-gcc.

I think this is happening.

[rleh]

32-bit Linux

Who uses 32-bit Linux today?

The Ubuntu PPA and Fedora include i386/i686 builds of avr-gcc and arm-none-eabi-gcc.

Oh, Raspberry Pi still has no official 64-bit software support 😒
Raspbian has no avr-gcc and arm-none-eabi-gcc packages, but Fedora has ARMv7 and Aarch64 packages of avr-gcc and arm-none-eabi-gcc.

[salkinium]

Oh, Raspberry Pi still has no official 64-bit software support 😒

Also missing x86 support 😒

[salkinium]

I think this is happening.

It happened.

[daniel-k]

\o/