[boost] PSA: Travis OS X bottleneck, <cxxstd> new Boost.Build feature

Subject: [boost] PSA: Travis OS X bottleneck, <cxxstd> new Boost.Build feature
From: Peter Dimov (lists_at_[hidden])
Date: 2017-10-26 16:43:51

Travis's OS X resources for open source projects seem to be insufficient, so 
OS X jobs are very slow and seem to be falling further and further behind. 
Therefore, library authors are encouraged to keep the OS X jobs to the 
minimum necessary. Spawning many OS X jobs takes hours (~25 minutes waiting 
time per job at a quick estimate).

On a not entirely unrelated note, Rene Rivera has added a new feature 
<cxxstd> to Boost.Build that controls the C++ standard in use. So for 
instance, instead of the old

    b2 libs/mylib/test toolset=gcc cxxflags=-std=c++11

one can now use

    b2 libs/mylib/test toolset=gcc cxxstd=11

In addition to being more convenient, this also allows several invocations 
to be combined into one:

    b2 libs/mylib/test toolset=clang cxxstd=03,11,14,1z

which can be leveraged to cut down on the number of jobs.

An example of using cxxstd in .travis.yml can be seen here:

https://github.com/boostorg/system/blob/develop/.travis.yml