[meta] Add table deep copy function.

meta.lua

@@ -35,4 +35,33 @@ function meta.mergetable(to, from)
     return to
 end
 
+--- Table deep copy.
+--
+-- Copy table 'obj', cloning any sub-table.
+-- Handles cyclic references.
+--
+-- @tparam table obj object to be copied
+-- @tparam[opt={}] table copied known copied sub-object table
+-- @treturn table newly created clone of 'obj'
+function meta.deepcopy(obj, copied)
+    copied = copied or {}
+
+    local r = {}
+
+    copied[obj] = r
+
+    for k,v in pairs(obj) do
+        if type(v) == 'table' then
+            local t = copied[v] or meta.deepcopy(v, copied)
+
+            copied[v] = t  -- NOP if object was already copied
+            v = t
+        end
+
+        r[k] = v
+    end
+
+    return r
+end
+
 return meta