C++ styleguide updated: mutable references and more

[Peter Kasting]

TLDR: The public Google C++ styleguide has been updated with a variety of changes, most significantly allowing mutable reference arguments.

Recently the public Google styleguide was updated with a number of significant changes.  Here are the biggest ones, and how they affect Chromium:

No effect:

• Google now gives C++17 as the preferred C++ version.  Chromium still uses C++14.  There is still no ETA for C++17 support; the most current status can always be found on Chromium's C++ version support page.

Affects Chromium but not Blink:

• For output and in/out parameters that cannot be null, Google now prefers mutable references, instead of pointers.  This is roughly equivalent to existing Blink style; the Blink styleguide has therefore been updated to remove mention of this, since it is no longer a divergence from Chromium style.  Note that return values are still preferred over output parameters, including when a function needs to return multiple values.

Affects Chromium and Blink:

• Function input parameters should not be const references if they must outlive the function call; use pointers-to-const instead (and document that they are non-null).
• Designated initializers are allowed when they use C++20-compliant syntax (I believe Clang will warn on noncompliant syntax).
• New enum values must use kCamelCase naming, not MACRO_STYLE (this was already preferred, but we previously allowed both).

Finally, this is a good time to remind people that DISALLOW_COPY_AND_ASSIGN is deprecated in new code; explicitly delete the copy/assign operators between your constructors and destructor.

As always, if you have questions or feedback about C++ style, send mail to c...@chromium.org and/or hop on the #cxx channel on the Chromium Slack.

PK

[Peter Kasting]

On Tue, Jun 2, 2020 at 3:19 PM Peter Kasting <pkas...@google.com> wrote:

• Google now gives C++17 as the preferred C++ version.  Chromium still uses C++14.  There is still no ETA for C++17 support; the most current status can always be found on Chromium's C++ version support page.
  

That last link should have gone to https://chromium-cpp.appspot.com/ .

PK 

[Michael Lippautz]

On Wed, Jun 3, 2020 at 12:19 AM 'Peter Kasting' via blink-dev <blin...@chromium.org> wrote:

Affects Chromium but not Blink:

• For output and in/out parameters that cannot be null, Google now prefers mutable references, instead of pointers.  This is roughly equivalent to existing Blink style; the Blink styleguide has therefore been updated to remove mention of this, since it is no longer a divergence from Chromium style.  Note that return values are still preferred over output parameters, including when a function needs to return multiple values.

Will this be applied globally (cpplint.py) or are we supposed to adjust dependent projects manually by adding "runtime/references" to a linter whitelist?