food_chain: X macro

cpp/food-chain/food_chain.cpp

@@ -6,9 +6,28 @@ namespace food_chain {
 
 using namespace std;
 
+#define ANIMAL_TABLE    \
+X(Fly,    "fly")        \
+X(Spider, "spider")     \
+X(Bird,   "bird")       \
+X(Cat,    "cat")        \
+X(Dog,    "dog")        \
+X(Goat,   "goat")       \
+X(Cow,    "cow")        \
+X(Horse,  "horse")
+
+#define X(a, b) a,
+enum Animal {
+      ANIMAL_TABLE
+};
+#undef X
+
+#define X(a, b) b,
+static const char *animal_name[] = {
+      ANIMAL_TABLE
+};
+#undef X
 
-static const char *animals[] = 
-    {"fly", "spider", "bird", "cat", "dog", "goat", "cow", "horse"};
 
 static const char *verse_phrase[] = {
     "",
@@ -21,8 +40,6 @@ static const char *verse_phrase[] = {
     "She's dead, of course!\n"
 };
 
-static const int size_of_animals = sizeof(animals) / sizeof(*animals);
-
 
 string verse(int index)
 {
@@ -31,27 +48,24 @@ string verse(int index)
     --index;
 
     result += string("I know an old lady who swallowed a ")
-       + animals[index]
+       + animal_name[index]
        + ".\n"
        + verse_phrase[index];
 
-    if (index != size_of_animals - 1) {
+    if (index != Animal::Horse) {
 
         for (int i = index; i > 0; --i) {
 
-            if (i == 2) {
+            result += string("She swallowed the ")
+               + animal_name[i]
+               + " to catch the "
+               + animal_name[i-1];
 
-                result += "She swallowed the bird to catch the spider "
+            if (i == Animal::Bird)
-                          "that wriggled and jiggled and tickled inside her.\n";
+                result += string(" that wriggled and jiggled and "
-            }
+                                 "tickled inside her");
-            else {
 
-                result += string("She swallowed the ")
+            result += string(".\n");
-                   + animals[i]
-                   + " to catch the "
-                   + animals[i-1]
-                   + ".\n";
-            }
         }
 
         result += "I don't know why she swallowed the fly. "