/usr/include/utilspp/singleton/ is in libcurlpp-dev 0.7.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/include/utilspp/singleton/CreationStatic.hpp
/usr/include/utilspp/singleton/CreationStatic.inl
/usr/include/utilspp/singleton/CreationUsingNew.hpp
/usr/include/utilspp/singleton/CreationUsingNew.inl
/usr/include/utilspp/singleton/LifetimeDefault.hpp
/usr/include/utilspp/singleton/LifetimeDefault.inl
/usr/include/utilspp/singleton/LifetimeLibrary.hpp
/usr/include/utilspp/singleton/LifetimeLibrary.inl
/usr/include/utilspp/singleton/LifetimeWithLongevity.hpp
/usr/include/utilspp/singleton/LifetimeWithLongevity.inl
/usr/include/utilspp/singleton/PrivateMembers.hpp
/usr/include/utilspp/singleton/PrivateMembers.inl
/usr/include/utilspp/singleton/SingletonHolder.hpp
/usr/include/utilspp/singleton/SingletonHolder.inl