error: No member std::ptr_fun in namespace std

Looks like I hit this while compiling as C++17, but nonetheless it's deprecated in C++11.

Oscillator.cxx.o.d -o examples/oscillator/CMakeFiles/Oscillator.dir/Oscillator.cxx.o -c ../examples/oscillator/Oscillator.cxx
../examples/oscillator/Oscillator.cxx:44:59: error: no member named 'ptr_fun' in namespace 'std'
          std::find_if(s.begin(), s.end(), std::not1(std::ptr_fun<int, int>(std::isspace))));
                                                     ~~~~~^

The fix is documented here.