/in/foo.cc:24:21: error: 'println' function uses 'auto' type specifier without trailing return type
 static auto println() {
                     ^
/in/foo.cc:24:21: note: deduced return type only available with -std=c++14 or -std=gnu++14
/in/foo.cc: In function 'auto println()':
/in/foo.cc:25:8: error: expected '(' before 'constexpr'
     if constexpr (format[0]=='%') {
        ^~~~~~~~~
/in/foo.cc:133:1: error: expected '}' at end of input
 }
 ^