[PATCH 1/1] all: add C99's "bool" define and encourage its use

[Thomas Haller <thaller redhat com>]

---
 Let's use bool.

 Comments?

 Thomas

 include/nm-default.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/include/nm-default.h b/include/nm-default.h
index d5c9d10..dc02763 100644
--- a/include/nm-default.h
+++ b/include/nm-default.h
@@ -70,4 +70,50 @@
 
 /*****************************************************************************/
 
+/**
+ * The boolean type _Bool is C99 but we mostly stick to C89. However, _Bool is too
+ * convinient to miss and is effectively available in gcc and clang. So, just use it.
+ *
+ * Usually, one would include "stdbool.h" to get the bool define which aliases
+ * _Bool. We provide this define here, because we want to make use of it anywhere.
+ * (also, stdbool.h is again C99).
+ *
+ * Using _Bool has advantages over gboolean:
+ *
+ * - commonly, _Bool is one byte large, instead of gboolean's 4 bytes (because gboolean
+ *   is a typedef for gint). Especially when having boolean fields in a struct, we can
+ *   thereby easily save some space.
+ *
+ * - _Bool type is guaranteed that two true expressions compare equal. E.g. the follwing
+ *   will not work:
+ *        gboolean v1 = 1;
+ *        gboolean v2 = 2;
+ *        g_assert_cmpint (v1, ==, v2); // will fail
+ *   For that, we often to use !! to coerce gboolean values to 0 or 1:
+ *        g_assert_cmpint (!!v2, ==, TRUE);
+ *   With _Bool this will be properly done by the compiler.
+ *
+ * - For structs, we might want to safe even more space and use bitfields:
+ *       struct s1 {
+ *           gboolean v1:1;
+ *       };
+ *   But the problem here is that gboolean is signed, so that
+ *   v1 will be either 0 or -1 (not 1, TRUE). Thus, the following
+ *   doesn't work:
+ *      struct s1 s = { .v1 = TRUE, };
+ *      g_assert_cmpint (s1.v1, ==, TRUE);
+ *   It will however work just fine with bool/_Bool.
+ *
+ * Also, add the defines for true/false. Those are nicely highlighted by the editor
+ * as special types, contrary to glib's TRUE/FALSE.
+ */
+
+#ifndef bool
+#define bool _Bool
+#define true    1
+#define false   0
+#endif
+
+/*****************************************************************************/
+
 #endif /* __NM_DEFAULT_H__ */
-- 
2.5.0