Minor Description
According to the google code style, the using should be used in internal namespace in header files. Grep the header files, only fetcher.hpp deserved a path.
You may use a using-declaration anywhere in a .cc file (including in the global namespace), and in functions, methods, classes, or within internal namespaces in .h files.
Do not use using-declarations in .h files except in explicitly marked internal-only namespaces, because anything imported into a namespace in a .h file becomes part of the public API exported by that file.
// OK in .cc files. // Must be in a function, method, internal namespace, or // class in .h files. using ::foo::bar;