update

learn_class/modern_C++_30/SFINAE/SFINAE.cpp

@@ -0,0 +1,41 @@
+//
+// Created by light on 20-1-5.
+//
+#include <iostream>
+
+using namespace std;
+
+template<typename T>
+class IsClassT {
+private:
+    typedef char One;
+    typedef struct {
+        char a[2];
+    } Two;
+
+    template<typename C>
+    static One test(int C::*);
+
+    // Will be chosen if T is anything except a class.
+    template<typename C>
+    static Two test(...);
+
+public:
+    enum {
+        Yes = sizeof(IsClassT<T>::test<T>(0)) == 1
+    };
+    enum {
+        No = !Yes
+    };
+};
+
+struct A {
+};
+
+int main() {
+    // 0不能转换为int int::*因为int不是类，所以它不能有成员指针。
+    cout << IsClassT<int>::Yes << endl;
+    cout << IsClassT<A>::Yes << endl;
+
+    return 0;
+}