Added metamacro_take(), to return the prefix of an argument list

jspahrsummers · Jun 20, 2012 · f7c3bee · f7c3bee
1 parent dc43cb3
commit f7c3bee
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diff --git a/include/metamacros.h b/include/metamacros.h
@@ -123,6 +123,13 @@
 #define metamacro_tail(...) \
         metamacro_tail_(__VA_ARGS__)
 
+/**
+ * Returns the first N (up to twenty) variadic arguments as a new argument list.
+ * At least N variadic arguments must be provided.
+ */
+#define metamacro_take(N, ...) \
+        metamacro_concat(metamacro_take, N)(__VA_ARGS__)
+
 /**
  * Decrements VAL, which must be a number between one and twenty, inclusive.
  *
@@ -641,4 +648,27 @@ metamacro_if_eq(0, 1)(true)(false)
 #define metamacro_if_eq_recursive19(VALUE) metamacro_if_eq_recursive18(metamacro_dec(VALUE))
 #define metamacro_if_eq_recursive20(VALUE) metamacro_if_eq_recursive19(metamacro_dec(VALUE))
 
+// metamacro_take expansions
+#define metamacro_take0(...)
+#define metamacro_take1(...) metamacro_head(__VA_ARGS__)
+#define metamacro_take2(...) metamacro_head(__VA_ARGS__), metamacro_take1(metamacro_tail(__VA_ARGS__))
+#define metamacro_take3(...) metamacro_head(__VA_ARGS__), metamacro_take2(metamacro_tail(__VA_ARGS__))
+#define metamacro_take4(...) metamacro_head(__VA_ARGS__), metamacro_take3(metamacro_tail(__VA_ARGS__))
+#define metamacro_take5(...) metamacro_head(__VA_ARGS__), metamacro_take4(metamacro_tail(__VA_ARGS__))
+#define metamacro_take6(...) metamacro_head(__VA_ARGS__), metamacro_take5(metamacro_tail(__VA_ARGS__))
+#define metamacro_take7(...) metamacro_head(__VA_ARGS__), metamacro_take6(metamacro_tail(__VA_ARGS__))
+#define metamacro_take8(...) metamacro_head(__VA_ARGS__), metamacro_take7(metamacro_tail(__VA_ARGS__))
+#define metamacro_take9(...) metamacro_head(__VA_ARGS__), metamacro_take8(metamacro_tail(__VA_ARGS__))
+#define metamacro_take10(...) metamacro_head(__VA_ARGS__), metamacro_take9(metamacro_tail(__VA_ARGS__))
+#define metamacro_take11(...) metamacro_head(__VA_ARGS__), metamacro_take10(metamacro_tail(__VA_ARGS__))
+#define metamacro_take12(...) metamacro_head(__VA_ARGS__), metamacro_take11(metamacro_tail(__VA_ARGS__))
+#define metamacro_take13(...) metamacro_head(__VA_ARGS__), metamacro_take12(metamacro_tail(__VA_ARGS__))
+#define metamacro_take14(...) metamacro_head(__VA_ARGS__), metamacro_take13(metamacro_tail(__VA_ARGS__))
+#define metamacro_take15(...) metamacro_head(__VA_ARGS__), metamacro_take14(metamacro_tail(__VA_ARGS__))
+#define metamacro_take16(...) metamacro_head(__VA_ARGS__), metamacro_take15(metamacro_tail(__VA_ARGS__))
+#define metamacro_take17(...) metamacro_head(__VA_ARGS__), metamacro_take16(metamacro_tail(__VA_ARGS__))
+#define metamacro_take18(...) metamacro_head(__VA_ARGS__), metamacro_take17(metamacro_tail(__VA_ARGS__))
+#define metamacro_take19(...) metamacro_head(__VA_ARGS__), metamacro_take18(metamacro_tail(__VA_ARGS__))
+#define metamacro_take20(...) metamacro_head(__VA_ARGS__), metamacro_take19(metamacro_tail(__VA_ARGS__))
+
 #endif
diff --git a/tests/metamacros_test.c b/tests/metamacros_test.c
@@ -27,6 +27,9 @@
 #define test_recursive_foreach(INDEX, VALUE) \
     metamacro_foreach_cxt_recursive(test_stringify_cxt,, "foo", (INDEX, VALUE))
 
+#define simple_concat(INDEX, STR) \
+    STR
+
 void metamacros_test (void) {
     assert(metamacro_at(0, -15) == -15);
     assert(metamacro_at(20, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -15) == -15);
@@ -112,4 +115,9 @@ void metamacros_test (void) {
     assert(0 == strcmp(metamacro_if_eq(0, 0)("A")(metamacro_if_eq_recursive(1, 1)("B")("C")), "A"));
     assert(0 == strcmp(metamacro_if_eq(0, 1)("A")(metamacro_if_eq_recursive(1, 1)("B")("C")), "B"));
     assert(0 == strcmp(metamacro_if_eq(0, 1)("A")(metamacro_if_eq_recursive(0, 1)("B")("C")), "C"));
+
+    assert(0 == strcmp(metamacro_foreach(simple_concat,, metamacro_take(1, "foo", "bar", "buzz")), "foo"));
+    assert(0 == strcmp(metamacro_foreach(simple_concat,, metamacro_take(3, "foo", "bar", "buzz")), "foobarbuzz"));
+    assert(0 == strcmp(metamacro_foreach(test_stringify,, metamacro_take(20, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)),
+        "001122334455667788991010111112121313141415151616171718181919"));
 }