tcon: routines for creating typesafe generic containers

[ccan] / ccan / tcon / tcon.h

diff --git a/ccan/tcon/tcon.h b/ccan/tcon/tcon.h
new file mode 100644 (file)
index 0000000..5b38c71
--- /dev/null
+++ b/ccan/tcon/tcon.h
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+/* Placed into the public domain */
+#ifndef CCAN_TCON_H
+#define CCAN_TCON_H
+#include "config.h"
+
+/**
+ * TCON - declare a _tcon type containing canary variables.
+ * @decls: the semi-colon separated list of type canaries.
+ *
+ * This declares a _tcon member for a structure.  It should be the
+ * last element in your structure; with sufficient compiler support it
+ * will not use any actual storage.  tcon_to_raw() will compare
+ * expressions with one of these "type canaries" to cause warnings if
+ * the container is misused.
+ *
+ * A type of "void *" will allow tcon_to_raw() to pass on any (pointer) type.
+ *
+ * Example:
+ *     // Simply typesafe linked list.
+ *     struct list_head {
+ *             struct list_head *prev, *next;
+ *     };
+ *
+ *     struct string_list {
+ *             struct list_head raw;
+ *             TCON(char *canary);
+ *     };
+ *
+ *     // More complex: mapping from one type to another.
+ *     struct map {
+ *             void *contents;
+ *     };
+ *
+ *     struct int_to_string_map {
+ *             struct map raw;
+ *             TCON(char *charp_canary; int int_canary);
+ *     };
+ */
+#if HAVE_FLEXIBLE_ARRAY_MEMBER
+#define TCON(decls) struct { decls; } _tcon[]
+#else
+#define TCON(decls) struct { decls; } _tcon[1]
+#endif
+
+/**
+ * tcon_check - typecheck a typed container
+ * @x: the structure containing the TCON.
+ * @canary: which canary to check against.
+ * @expr: the expression whose type must match the TCON (not evaluated)
+ *
+ * This macro is used to check that the expression is the type
+ * expected for this structure (note the "useless" sizeof() argument
+ * which contains this comparison with the type canary).
+ *
+ * It evaluates to @x so you can chain it.
+ *
+ * Example:
+ *     #define tlist_add(h, n, member) \
+ *             list_add(&tcon_check((h), canary, (n))->raw, &(n)->member)
+ */
+#define tcon_check(x, canary, expr)                            \
+       (sizeof((x)->_tcon[0].canary == (expr)) ? (x) : (x))
+
+
+/**
+ * tcon_cast - cast to a canary type for this container (or void *)
+ * @x: a structure containing the TCON.
+ * @canary: which canary to cast to.
+ * @expr: the value to cast
+ *
+ * This is used to cast to the correct type for this container.  If the
+ * platform doesn't HAVE_TYPEOF, then it casts to void * (which will
+ * cause a warning if the user doesn't expect a pointer type).
+ */
+#if HAVE_TYPEOF
+#define tcon_cast(x, canary, expr) ((__typeof__((x)->_tcon[0].canary))(expr))
+#else
+#define tcon_cast(x, canary, expr) ((void *)(expr))
+#endif
+
+#endif /* CCAN_TCON_H */