Update 007_any_any_cast.cpp

Author: ls-Brynn

cpp_17/007_any_any_cast.cpp

@@ -1 +1,48 @@
-1
+#include <string>
+#include <iostream>
+#include <any>
+#include <utility>
+ 
+int main()
+{
+    // simple example 
+ 
+    auto a = std::any(12);
+ 
+    std::cout << std::any_cast<int>(a) << '\n'; 
+ 
+    try {
+        std::cout << std::any_cast<std::string>(a) << '\n';
+    }
+    catch(const std::bad_any_cast& e) {
+        std::cout << e.what() << '\n';
+    }
+ 
+    // pointer example
+ 
+    if (int* i = std::any_cast<int>(&a)) {
+       std::cout << "a is int: " << *i << '\n';
+    } else if (std::string* s = std::any_cast<std::string>(&a)) {
+       std::cout << "a is std::string: " << *s << '\n';
+    } else {
+       std::cout << "a is another type or unset\n";
+    }
+ 
+    // advanced example
+ 
+    a = std::string("hello");
+ 
+    auto& ra = std::any_cast<std::string&>(a); //< reference
+    ra[1] = 'o';
+ 
+    std::cout << "a: "
+        << std::any_cast<const std::string&>(a) << '\n'; //< const reference
+ 
+    auto b = std::any_cast<std::string&&>(std::move(a)); //< rvalue reference
+ 
+    // Note: 'b' is a move-constructed std::string,
+    // 'a' is left in valid but unspecified state
+ 
+    std::cout << "a: " << *std::any_cast<std::string>(&a) //< pointer
+        << "b: " << b << '\n';
+}