An interface and safety. In C++ the template's arguments are directly copied into it's body. A module can only be accessed via its interface. This in turn allow

An interface and safety. In C++ the template's arguments are directly copied into it's body. A module can only be accessed via its interface. This in turn allows for a typechecker to guarantee the absence of certain errors. It also enables separate compilation that you do not have for C++ template's. The downside is of course that a C++ compiler can apply more optimizations. As a side note: the argument, I can do X with Y so why use Z is somewhat misleading, when Y and Z are both Turing complete ;).