Procs
proc initCppPair[T1, T2](): CppPair[T1, T2] {.constructor, importcpp: "\'0(@)", header: "<utility>".}
proc initCppPair[T1, T2](p: CppPair[T1, T2]): CppPair[T1, T2] {.constructor, importcpp: "\'0(@)", header: "<utility>".}
proc initCppPair[T1, T2](x: T1; y: T2): CppPair[T1, T2] {.constructor, importcpp: "\'0(@)", header: "<utility>".}