Allow getting a tree entry by position

c_src/geef.c

@@ -163,6 +163,7 @@ static ErlNifFunc geef_funcs[] =
 	{"commit_tree", 1, geef_commit_tree},
 	{"commit_tree_id", 1, geef_commit_tree_id},
 	{"tree_bypath", 2, geef_tree_bypath},
+	{"tree_nth",     2, geef_tree_nth},
 	{"blob_size", 1, geef_blob_size},
 	{"blob_content", 1, geef_blob_content},
 	{"tag_peel", 1, geef_tag_peel},

c_src/tree.c

@@ -59,3 +59,24 @@ geef_tree_bypath(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
 	enif_release_binary(&bin);
 	return tree_entry_to_term(env, entry);
 }
+
+ERL_NIF_TERM
+geef_tree_nth(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
+{
+	geef_object *obj;
+	const git_tree_entry *entry;
+	unsigned int nth;
+
+	if (!enif_get_resource(env, argv[0], geef_object_type, (void **) &obj))
+		return enif_make_badarg(env);
+
+	if (!enif_get_uint(env, argv[1], &nth))
+		return enif_make_badarg(env);
+
+	entry = git_tree_entry_byindex((git_tree *)obj->obj, nth);
+
+	if (!entry)
+		return geef_error(env);
+
+	return tree_entry_to_term(env, entry);
+}

c_src/tree.h

@@ -4,5 +4,6 @@
 #include "object.h"
 
 ERL_NIF_TERM geef_tree_bypath(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
+ERL_NIF_TERM geef_tree_nth(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
 
 #endif