Merge branch 'bugfix/compile-error-and-warnings-with-gcc-8' into 'master'
fix compile error and several warnings with gcc 8
See merge request !216 (merged)
(cherry picked from commit 33b9cb42)
ae1ec50a CompPair: make operator()
a const method
bad3dd33 do not catch polymorphic types by value
7fea4b07 silence warnings about unused variables