lib/: Pure C machinery for handling `keyword arguments' to functions.

[sod] / lib / sod.h

diff --git a/lib/sod.h b/lib/sod.h
index 919b92743874fc016b925014e15aa069a19076d3..2705dcc71c0c27a976b2145945e289aa348890a1 100644 (file)
--- a/lib/sod.h
+++ b/lib/sod.h
@@ -7,7 +7,7 @@
 
 /*----- Licensing notice --------------------------------------------------*
  *
- * This file is part of the Sensble Object Design, an object system for C.
+ * This file is part of the Sensible Object Design, an object system for C.
  *
  * The SOD Runtime Library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public License as
@@ -32,11 +32,69 @@
   extern "C" {
 #endif
 
+/*----- Preliminary utilities ---------------------------------------------*/
+
+/* --- @SOD__HAVE_VARARGS_MACROS@ --- *
+ *
+ * Use:                Defined if the compiler supports C99-style variadic macros.
+ *
+ *             This is more complicated than just checking the value of
+ *             @__STDC_VERSION__@ because GCC has traditionally claimed C89
+ *             by default, but provides the functionality anyway unless it's
+ *             been explicitly turned off.
+ */
+
+#if __STDC_VERSION__ >= 199901
+   /* The feature exists.  All is well with the world. */
+
+#  define SOD__HAVE_VARARGS_MACROS
+
+#elif __GNUC__ >= 3
+   /* We're using GCC, which is trying to deny it but we don't believe it.
+    * Unfortunately there's a fly in the ointment: if `-pedantic' -- or,
+    * worse, `-pedantic-errors' -- is set, then GCC will warn about these
+    * macros being defined, and there isn't a way to detect pedantry from the
+    * preprocessor.
+    *
+    * We must deploy bodges.  There doesn't seem to be a good way to suppress
+    * particular warnings from the preprocessor: in particular, messing about
+    * with `pragma GCC diagnostic' doesn't help.  So we're left with this
+    * hack: just declare all Sod-generated header files which try to do
+    * varargs macro things to be `system headers', which means that GCC's
+    * preprocessor will let them get away with all manner of nefarious stuff.
+    */
+
+#  define SOD__HAVE_VARARGS_MACROS
+#  define SOD__VARARGS_MACROS_PREAMBLE _Pragma("GCC system_header")
+
+#endif
+
+/* Make sure this gratuitous hack is understood, at least vacuously. */
+#ifndef SOD__VARARGS_MACROS_PREAMBLE
+#  define SOD__VARARGS_MACROS_PREAMBLE
+#endif
+
+/* We're going to want to make use of this ourselves. */
+SOD__VARARGS_MACROS_PREAMBLE
+
+/* --- @SOD__CAR@ --- *
+ *
+ * Arguments:  @...@ = a nonempty list of arguments
+ *
+ * Returns:    The first argument only.
+ */
+
+#ifdef SOD__HAVE_VARARGS_MACROS
+#  define SOD__CAR(...) SOD__CARx(__VA_LIST__, _)
+#  define SOD__CARx(a, ...) a
+#endif
+
 /*----- Header files ------------------------------------------------------*/
 
 #include <stdarg.h>
 #include <stddef.h>
 
+#include "keyword.h"
 #include "sod-base.h"
 
 /*----- Data structures ---------------------------------------------------*/
@@ -53,7 +111,7 @@ struct sod_vtable {
  * these.
  */
 struct sod_instance {
-  struct sod_vtable *_vt;              /* Pointer to (chain's) vtable */
+  const struct sod_vtable *_vt;                /* Pointer to (chain's) vtable */
 };
 
 /* Information about a particular chain of superclasses.  In each class,
@@ -76,14 +134,15 @@ struct sod_chain {
  * Arguments:  @chead@ = nickname of target chain's head
  *             @obj@ = pointer to an instance chain
  *
- * Returns:    Pointer to target chain, as a @char *@.
+ * Returns:    Pointer to target chain, as a @void *@.
  *
  * Use:                Utility for implementing cross-chain upcasts.  It's probably
  *             not that clever to use this macro directly; it's used to make
  *             the automatically-generated upcast macros more palatable.
  */
 
-#define SOD_XCHAIN(chead, obj) ((char *)(obj) + (obj)->_vt->_off_##chead)
+#define SOD_XCHAIN(chead, obj)                                         \
+  ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
 
 /* --- @SOD_OFFSETDIFF@ --- *
  *
@@ -130,7 +189,7 @@ struct sod_chain {
  *
  * Arguments:  @p@ = pointer to an instance chain
  *
- * Returns:    A pointer to the instance's class, as a const SodClass.
+ * Returns:    A pointer to the instance's class, as a @const SodClass *@.
  */
 
 #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)