Add. class.super function to implement inheritance.

```Lua
local Foo = ut.class()
local Boo = ut.class(Foo) do
local super = ut.class.super(Boo)
function Boo:__init() self = super(self, '__init') end
end
```

src/lua/lluv/luasocket.lua

@@ -213,11 +213,12 @@ end
 
 ----------------------------------------------------------------------------
 local TcpSock = ut.class(BaseSock) do
+local super = ut.class.super(TcpSock)
 
 local MAX_ACCEPT_COUNT = 10
 
 function TcpSock:__init(s)
-  assert(TcpSock.__base.__init(self))
+  self = assert(super(self, '__init'))
 
   self._buf   = assert(ut.Buffer.new("\r*\n", true))
 
@@ -427,9 +428,10 @@ end
 
 ----------------------------------------------------------------------------
 local UdpSock = ut.class(BaseSock) do
+local super = ut.class.super(UdpSock)
 
 function UdpSock:__init(s)
-  assert(UdpSock.__base.__init(self))
+  self = assert(super(self, '__init'))
 
   self._buf   = assert(ut.Queue.new())
 

src/lua/lluv/utils.lua

@@ -98,6 +98,25 @@ local function class_self_test()
   B.new(1, 2, 3)
 end
 
+-------------------------------------------------------------------
+local Class = {} do
+
+setmetatable(Class, {__call = function(_, ...) return class(...) end})
+
+local function super(class, self, method, ...)
+  if class.__base and class.__base[method] then
+    return class.__base[method](self, ...)
+  end
+  if method == '__init' then return self end
+end
+
+function Class.super(class)
+  return function(...) return super(class, ...) end
+end
+
+end
+-------------------------------------------------------------------
+
 -------------------------------------------------------------------
 local corun do
 
@@ -895,7 +914,7 @@ return {
   List        = List;
   Errors      = MakeErrors;
   DeferQueue  = DeferQueue;
-  class       = class;
+  class       = Class;
   split_first = split_first;
   split       = split;
   usplit      = usplit;