tal/autoptr: new module.

[ccan] / ccan / tal / autoptr / autoptr.h

diff --git a/ccan/tal/autoptr/autoptr.h b/ccan/tal/autoptr/autoptr.h
new file mode 100644 (file)
index 0000000..5799665
--- /dev/null
+++ b/ccan/tal/autoptr/autoptr.h
@@ -0,0 +1,47 @@
+/* MIT (BSD) license - see LICENSE file for details */
+#ifndef CCAN_TAL_AUTOPTR_H
+#define CCAN_TAL_AUTOPTR_H
+#include <ccan/tal/tal.h>
+
+struct autonull;
+
+/**
+ * autonull_set_ptr - set a pointer, NULL it when pointer tal_free'd.
+ * @ctx: the tal context which owns this autonull.
+ * @pp: pointer to tal pointer
+ * @p: the tal pointer to set *@pp to.
+ *
+ * *@pp is set to @p.  When @p is tal_free'd directly or indirectly, *@pp will
+ * be set to NULL.  Or, if the returned object is freed, the callback is
+ * deactivated.
+ *
+ * Example:
+ *     struct parent {
+ *             struct child *c;
+ *     };
+ *     struct child {
+ *             const char *name;
+ *     };
+ *
+ *     int main(void)
+ *     {
+ *             struct parent *p = tal(NULL, struct parent);
+ *             struct child *c = tal(p, struct child);
+ *             c->name = "Child";
+ *
+ *             autonull_set_ptr(p, &p->c, c);
+ *             assert(p->c == c);
+ *
+ *             // Automatically clears p->c.
+ *             tal_free(c);
+ *             assert(p->c == NULL);
+ *             return 0;
+ *     }
+ *
+ */
+#define autonull_set_ptr(ctx, pp, p)           \
+       autonull_set_ptr_((ctx), (pp) + 0*sizeof(*(pp) = (p)), (p))
+
+struct autonull *autonull_set_ptr_(const tal_t *ctx, void *pp, const tal_t *p);
+
+#endif /* CCAN_TAL_AUTOPTR_H */