Calculate factorial using template compilation

//////////////////////////////////////// /// // C ++ templates meta programming template <bool, typename T1, typename T2> struct If {typedef T1 type ;}; template <typename T1, typename T2> struct If <false, typename T1, typename T2 >{ typedef T2 type ;}; template <int n> struct Factorial_exception {enum {Value =-1 };}; template <int n> struct _ Factorial {enum {Value = n * _ Factorial <n-1> :: Value };}; template <> struct _ Factorial <0 >{ enum {Value = 1 };}; // final result template <int n> struct Factorial {enum {Value = If <n <1, Factorial_exception <n>/* When the Value is less than 1, the Factorial is-1 */, _ Factorial <n >:: type: Value };}; example: int I = Factorial <-2 >:: Value; // The compiled assembly code for this statement is mov dword ptr [I], 0 FFFFFFFFh amazing?