Merge pull request #758 from Eliyahu-Ravuna/patch-22

Short string optimization example for C.180

CppCoreGuidelines.md

@@ -7322,7 +7322,44 @@ But heed the warning: [Avoid "naked" `union`s](#Ru-naked)
 
 ##### Example
 
-    ??? short-string optimization; safe union without dscriminant ???
+    // Short string optimization
+    
+    constexpr size_t buffer_size = 16; // Slightly larger than the size of a pointer
+    
+    class Immutable_string {
+    public:
+        Immutable_string(const char* str) :
+            size(strlen(str))
+        {
+            if (size < buffer_size)
+                strcpy_s(string_buffer, buffer_size, str);
+            else {
+                string_ptr = new char[size + 1];
+                strcpy_s(string_ptr, size + 1, str);
+            }
+        }
+    
+        ~Immutable_string()
+        {
+            if (size >= buffer_size)
+                delete string_ptr;
+        }
+    
+        const char* get_str() const
+        {
+            return (size < buffer_size) ? string_buffer : string_ptr;
+        }
+    
+    private:
+        // If the string is short enough, we store the string itself
+        // instead of a pointer to the string.
+        union {
+            char* string_ptr;
+            char string_buffer[buffer_size];
+        };
+    
+        const size_t size;
+    };
 
 ##### Enforcement