58 lines
1.3 KiB
C++
58 lines
1.3 KiB
C++
//
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// Created by light on 20-1-5.
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//
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#include <iostream>
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using namespace std;
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// 使用template实现while循环
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template <bool condition, typename Body> struct WhileLoop;
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template <typename Body> struct WhileLoop<true, Body> {
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typedef
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typename WhileLoop<Body::cond_value, typename Body::next_type>::type type;
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};
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template <typename Body> struct WhileLoop<false, Body> {
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typedef typename Body::res_type type;
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};
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template <typename Body> struct While {
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typedef typename WhileLoop<Body::cond_value, Body>::type type;
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};
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template <typename Body> using While_t = WhileLoop<Body::cond_value, Body>;
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namespace my {
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template <class T, T v> struct integral_constant {
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static const T value = v;
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typedef T value_type;
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typedef integral_constant<T, v> type;
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};
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} // namespace my
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template <int result, int n> struct SumLoop {
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// 循环的条件
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static const bool cond_value = n != 0;
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// 循环后的结果
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static const int res_value = result;
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// 循环时的状态
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typedef my::integral_constant<int, res_value> res_type;
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// 循环执行一次时的状态
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typedef SumLoop<result + n, n - 1> next_type;
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};
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template <int n> struct Sum { typedef SumLoop<0, n> type; };
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template <int n> using Sum_t = SumLoop<0, n>;
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int main() {
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cout << While<Sum<6>::type>::type::value << endl;
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cout << While_t<Sum_t<6>>::type::value << endl;
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return 0;
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}
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