strmap: new utility functions

Add strmap as a new struct and associated utility functions,
specifically for hashmaps that map strings to some value.  The API is
taken directly from Peff's proposal at
https://lore.kernel.org/git/20180906191203.GA26184@sigill.intra.peff.net/

Note that similar string-list, I have a strdup_strings setting.
However, unlike string-list, strmap_init() does not take a parameter for
this setting and instead automatically sets it to 1; callers who want to
control this detail need to instead call strmap_init_with_options().
(Future patches will add additional parameters to
strmap_init_with_options()).

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/strmap.h b/strmap.h
new file mode 100644
index 0000000000..96888c23ad
--- /dev/null
+++ b/strmap.h
@@ -0,0 +1,65 @@
+#ifndef STRMAP_H
+#define STRMAP_H
+
+#include "hashmap.h"
+
+struct strmap {
+	struct hashmap map;
+	unsigned int strdup_strings:1;
+};
+
+struct strmap_entry {
+	struct hashmap_entry ent;
+	const char *key;
+	void *value;
+};
+
+int cmp_strmap_entry(const void *hashmap_cmp_fn_data,
+		     const struct hashmap_entry *entry1,
+		     const struct hashmap_entry *entry2,
+		     const void *keydata);
+
+#define STRMAP_INIT { \
+			.map = HASHMAP_INIT(cmp_strmap_entry, NULL),  \
+			.strdup_strings = 1,                          \
+		    }
+
+/*
+ * Initialize the members of the strmap.  Any keys added to the strmap will
+ * be strdup'ed with their memory managed by the strmap.
+ */
+void strmap_init(struct strmap *map);
+
+/*
+ * Same as strmap_init, but for those who want to control the memory management
+ * carefully instead of using the default of strdup_strings=1.
+ */
+void strmap_init_with_options(struct strmap *map,
+			      int strdup_strings);
+
+/*
+ * Remove all entries from the map, releasing any allocated resources.
+ */
+void strmap_clear(struct strmap *map, int free_values);
+
+/*
+ * Insert "str" into the map, pointing to "data".
+ *
+ * If an entry for "str" already exists, its data pointer is overwritten, and
+ * the original data pointer returned. Otherwise, returns NULL.
+ */
+void *strmap_put(struct strmap *map, const char *str, void *data);
+
+/*
+ * Return the data pointer mapped by "str", or NULL if the entry does not
+ * exist.
+ */
+void *strmap_get(struct strmap *map, const char *str);
+
+/*
+ * Return non-zero iff "str" is present in the map. This differs from
+ * strmap_get() in that it can distinguish entries with a NULL data pointer.
+ */
+int strmap_contains(struct strmap *map, const char *str);
+
+#endif /* STRMAP_H */