support bazel complie this project and format code.

learn_class/modern_cpp_30/reference/forward.cpp

@@ -0,0 +1,45 @@
+//
+// Created by light on 19-12-15.
+//
+#include <iostream>
+#include "shape.h"
+
+void overloaded( int const &arg ) { std::cout << "by lvalue\n"; }
+void overloaded( int && arg ) { std::cout << "by rvalue\n"; }
+
+template< typename t >
+/* "t &&" with "t" being template param is special, and  adjusts "t" to be
+   (for example) "int &" or non-ref "int" so std::forward knows what to do. */
+void forwarding( t && arg ) {
+    std::cout << "via std::forward: ";
+    overloaded( std::forward< t >( arg ) );
+    std::cout << "via std::move: ";
+    overloaded( std::move( arg ) ); // conceptually this would invalidate arg
+    std::cout << "by simple passing: ";
+    overloaded( arg );
+}
+void foo(const shape&)
+{
+    puts("foo(const shape&)");
+}
+void foo(shape&&)
+{
+    puts("foo(shape&&)");
+}
+template <typename T>
+void bar(T&& s)
+{
+    foo(std::forward<T>(s));
+}
+int main() {
+    std::cout << "initial caller passes rvalue:\n";
+    forwarding( 5 );
+    std::cout << "initial caller passes lvalue:\n";
+    int x = 5;
+    forwarding( x );
+
+    circle temp;
+    bar(temp);
+    bar(circle());
+
+}