an Vector<T>'; } ! ! hh_client /home/vagrant/test.hh:3:22,22: You probably forgot to bind this type parameter right? Add <T> somewhere (after the function name definition, or after the class name) Examples: function foo<T> or class A<T> /home/vagrant/test.hh:4:10,27: Invalid return type /home/vagrant/test.hh:3:15,20: This is an object of type Vector /home/vagrant/test.hh:4:10,27: It is incompatible with a string