如何在编译时驱动C＃，C ++或Java编译器来计算1 + 2 + 3 +…+ 1000？

如何在编译时驱动C＃，C ++或Java编译器来计算1 + 2 + 3 +…+ 1000？

*立即 *更新， 具有改进的递归深度！无需增加深度即可在MSVC10和GCC上运行。:)

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简单的编译时递归+加法：

template<unsigned Cur, unsigned Goal>struct adder{  static unsigned const sub_goal = (Cur + Goal) / 2;  static unsigned const tmp = adder<Cur, sub_goal>::value;  static unsigned const value = tmp + adder<sub_goal+1, Goal>::value;};template<unsigned Goal>struct adder<Goal, Goal>{  static unsigned const value = Goal;};

测试码：

template<unsigned Start>struct sum_from{  template<unsigned Goal>  struct to{    template<unsigned N>    struct equals;    typedef equals<adder<Start, Goal>::value> result;  };};int main(){  sum_from<1>::to<1000>::result();}

GCC的输出：

错误：声明’struct sum_from <1u> :: to <1000u> :: equals <500500u>’

有关Ideone的现场示例。

MSVC10的输出：

error C2514: 'sum_from<Start>::to<Goal>::equals<Result>' : class has no constructors      with      [          Start=1,          Goal=1000,          Result=500500      ]