Merge branch 'compiler_error_fix' into 'master'

Compiler error fix

Closes #18 

See merge request !42
6 jobs for master
Status Name Job ID Coverage
  Test
passed clang-c++11 #1845
Linux

00:22:53

passed clang-c++98 #1847
Linux

00:17:11

passed gcc-c++11 #1844
Linux

00:04:46

passed gcc-c++98 #1846
Linux

00:03:54

passed macos-c++11 #1848
Apple

00:15:27

passed macos-c++98 #1849
Apple

00:08:28