list: Allow list_front(), list_back() to take 'const' arguments.

It totally makes sense to pass a const struct list * to one of these
functions.  Ideally the return type would be the same as the argument
type but C can't handle that, so this is the best second choice.

1 files changed, 10 insertions, 6 deletions

diff --git a/lib/list.c b/lib/list.c
index 6d5f6fe0..0f4f2f84 100644
--- a/lib/list.c
+++ b/lib/list.c
@@ -127,20 +127,24 @@ list_pop_back(struct list *list)
     return back;
 }
 
-/* Returns the front element in 'list'.
-   Undefined behavior if 'list' is empty. */
+/* Returns the front element in 'list_'.
+   Undefined behavior if 'list_' is empty. */
 struct list *
-list_front(struct list *list)
+list_front(const struct list *list_)
 {
+    struct list *list = (struct list *) list_;
+
     assert(!list_is_empty(list));
     return list->next;
 }
 
-/* Returns the back element in 'list'.
-   Undefined behavior if 'list' is empty. */
+/* Returns the back element in 'list_'.
+   Undefined behavior if 'list_' is empty. */
 struct list *
-list_back(struct list *list)
+list_back(const struct list *list_)
 {
+    struct list *list = (struct list *) list_;
+
     assert(!list_is_empty(list));
     return list->prev;
 }