message: Travis CI compiler versions
diff: -language: cpp
  +language: gneric
  sudo: required
  os: linux
  dist: trusty
  matrix:
  include:
  - # works on Precise and Trusty
  - os: linux
  + env: COMPILER_NAME=gcc CXX=g++-7 CC=gcc-7
  addons:
  apt:
  + packages:
  + - g++-7
  sources:
  - ubuntu-toolchain-r-test
  + - os: linux
  + env: COMPILER_NAME=clang CXX=clang++-5.0 CC=clang-5.0
  + addons:
  + apt:
  packages:
  - - g++-7
  - env:
  - - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
  -before_install:
  - - eval "${MATRIX_EVAL}"
  + - clang-5.0
  + sources: *sources
  compiler:
  - clang
  - gcc
  