book: translate ch03

see #12

code/3/3.2.function.wrap.cpp

@@ -0,0 +1,51 @@
+//
+// 3.2.function.wrap.cpp
+// chapter 03 runtime enhancement
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <functional>
+#include <iostream>
+
+using foo = void(int);  // function pointer
+void functional(foo f) {
+    f(1);
+}
+
+int foo2(int para) {
+    return para;
+}
+
+int foo3(int a, int b, int c) {
+    return 0;
+}
+
+int main() {
+
+    auto f = [](int value) {
+        std::cout << value << std::endl;
+    };
+    functional(f);  // call by function pointer
+    f(1);           // call by lambda expression
+
+    // std::function wraps a function that take int paremeter and returns int value
+    std::function<int(int)> func = foo2;
+
+    int important = 10;
+    std::function<int(int)> func2 = [&](int value) -> int {
+        return 1+value+important;
+    };
+    std::cout << func(10) << std::endl;
+    std::cout << func2(10) << std::endl;
+
+    // bind parameter 1, 2 on function foo, and use std::placeholders::_1 as placeholder
+    // for the first parameter.
+    auto bindFoo = std::bind(foo3, std::placeholders::_1, 1,2);
+    // when call bindFoo, we only need one param left
+    bindFoo(1);
+
+    return 0;
+}