48 lines
1.3 KiB
C++
48 lines
1.3 KiB
C++
//
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// Created by light on 20-1-6.
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//
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#include <iostream>
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#include "structData.h"
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template<class T>
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struct hasSerialize {
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// We test if the type has serialize using decltype and declval.
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// decltype将根据逗号表达式选择最后一个类型作为返回值
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// 如果C有serialize将调用当前版本,没有serialize,则失败,此时编译时不报错,继续寻找重载函数,也就是SFINAE.
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template<typename C>
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static constexpr decltype(std::declval<C>().serialize(), bool()) test(int /* unused */) {
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// We can return values, thanks to constexpr instead of playing with sizeof.
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return true;
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}
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template<typename C>
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static constexpr bool test(...) {
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return false;
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}
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// int is used to give the precedence!
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static constexpr bool value = test<T>(int());
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};
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template<class T>
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std::string serialize(const T &obj) {
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// 不加constexpr 报错：error: no member named 'serialize' in 'A'.
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if constexpr (hasSerialize<T>::value)
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return obj.serialize();
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else
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return to_string(obj);
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}
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int main() {
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A a;
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B b;
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C c;
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// The following lines work like a charm!
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std::cout << serialize(a) << std::endl;
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std::cout << serialize(b) << std::endl;
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std::cout << serialize(c) << std::endl;
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} |