string-list: add string_list_{pop, last} functions

Commit Message

Stefan Beller Sept. 21, 2018, 10:08 p.m. UTC

Add a few functions to allow a string-list to be used as a stack:

 - string_list_last() lets a caller peek the string_list_item at the
   end of the string list.  The caller needs to be aware that it is
   borrowing a pointer, which can become invalid if/when the
   string_list is resized.

 - string_list_pop() removes the string_list_item at the end of
   the string list.

 - there is no string_list_push(); string_list_append() can be used
   in its place.

You can use them in this pattern:

    while (list.nr) {
        struct string_list_item *item = string_list_last(&list);

        work_on(item);
        string_list_pop(&list, free_util);
    }

Helped-by: Junio C Hamano <[e-mail]>
Signed-off-by: Stefan Beller <[e-mail]>
---

I will be resending this series shortly, but it will not contain this patch,
as I will have no need for these any longer.

For the record, this is the final state of this patch.
It may be useful on its own.

Thanks,
Stefan

 string-list.c | 14 ++++++++++++++
 string-list.h | 15 +++++++++++++++
 2 files changed, 29 insertions(+)

Patch

diff --git a/string-list.c b/string-list.c
index 771c4550980..04db2b537c0 100644
--- a/string-list.c
+++ b/string-list.c
@@ -80,6 +80,20 @@  void string_list_remove(struct string_list *list, const char *string,
 	}
 }
 
+void string_list_pop(struct string_list *list, int free_util)
+{
+	if (list->nr == 0)
+		BUG("tried to remove an item from empty string list");
+
+	if (list->strdup_strings)
+		free(list->items[list->nr - 1].string);
+
+	if (free_util)
+		free(list->items[list->nr - 1].util);
+
+	list->nr--;
+}
+
 int string_list_has_string(const struct string_list *list, const char *string)
 {
 	int exact_match;
diff --git a/string-list.h b/string-list.h
index ff8f6094a33..15f2936e337 100644
--- a/string-list.h
+++ b/string-list.h
@@ -191,6 +191,21 @@  extern void string_list_remove(struct string_list *list, const char *string,
  */
 struct string_list_item *string_list_lookup(struct string_list *list, const char *string);
 
+/**
+ * Removes the last item from the list.
+ * The caller must ensure that the list is not empty.
+ */
+void string_list_pop(struct string_list *list, int free_util);
+
+/*
+ * Returns the last item of the list. As it returns the raw access, do not
+ * modify the list while holding onto the returned pointer.
+ */
+static inline struct string_list_item *string_list_last(struct string_list *list)
+{
+	return &list->items[list->nr - 1];
+}
+
 /*
  * Remove all but the first of consecutive entries with the same
  * string value.  If free_util is true, call free() on the util