support bazel complie this project and format code.

learn_class/modern_cpp_30/SFINAE/sfinae paper/blending1.cpp

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+//
+// Created by light on 20-1-6.
+//
+
+#include <iostream>
+#include "structData.h"
+
+
+template<class T>
+struct hasSerialize {
+    // We test if the type has serialize using decltype and declval.
+    // decltype将根据逗号表达式选择最后一个类型作为返回值
+    // 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.
+    template<typename C>
+    static constexpr decltype(std::declval<C>().serialize(), bool()) test(int /* unused */) {
+        // We can return values, thanks to constexpr instead of playing with sizeof.
+        return true;
+    }
+
+    template<typename C>
+    static constexpr bool test(...) {
+        return false;
+    }
+
+    // int is used to give the precedence!
+    static constexpr bool value = test<T>(int());
+};
+
+template<class T>
+std::string serialize(const T &obj) {
+    // 不加constexpr 报错：error: no member named 'serialize' in 'A'.
+    if constexpr (hasSerialize<T>::value)
+        return obj.serialize();
+    else
+        return to_string(obj);
+}
+
+int main() {
+    A a;
+    B b;
+    C c;
+
+    // The following lines work like a charm!
+    std::cout << serialize(a) << std::endl;
+    std::cout << serialize(b) << std::endl;
+    std::cout << serialize(c) << std::endl;
+
+}