support bazel complie this project and format code.

learn_class/modern_cpp_30/constexpr/test3.cpp

@@ -0,0 +1,25 @@
+//
+// Created by light on 20-1-10.
+//
+
+#include <iostream>
+
+class test3 {
+public:
+  int value;
+
+  // constexpr const method - can't chanage the values of object fields and can
+  // be evaluated at compile time.
+  constexpr int getvalue() const { return (value); }
+
+  constexpr test3(int Value) : value(Value) {}
+};
+
+int main() {
+
+  // 加不加都行
+  constexpr test3 x(100); // OK. Constructor is constexpr.
+
+  int array[x.getvalue()]; // OK. x.getvalue() is constexpr and can be evaluated
+                           // at compile time.
+}