util.set: Add is_set() to test if an object is a set

1 files changed, 8 insertions, 2 deletions

diff --git a/util/set.lua b/util/set.lua
index 02fabc6a..b7345e7e 100644
--- a/util/set.lua
+++ b/util/set.lua
@@ -6,8 +6,8 @@
 -- COPYING file in the source package for more information.
 --
 
-local ipairs, pairs, setmetatable, next, tostring =
-      ipairs, pairs, setmetatable, next, tostring;
+local ipairs, pairs, getmetatable, setmetatable, next, tostring =
+      ipairs, pairs, getmetatable, setmetatable, next, tostring;
 local t_concat = table.concat;
 
 local _ENV = nil;
@@ -31,6 +31,11 @@ function set_mt:__freeze()
 	return a;
 end
 
+local function is_set(o)
+	local mt = getmetatable(o);
+	return mt == set_mt;
+end
+
 local function new(list)
 	local items = setmetatable({}, items_mt);
 	local set = { _items = items };
@@ -171,6 +176,7 @@ end
 
 return {
 	new = new;
+	is_set = is_set;
 	union = union;
 	difference = difference;
 	intersection = intersection;