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            的筆記

            隨時隨地編輯

            Metatables

            參考資料

            Referenced Values, Metatables, and Simple Inheritance>

            http://phrogz.net/lua/LearningLua_ValuesAndMetatables.html

            Metatable In Lua 淺嘗輒止
            http://www.cnblogs.com/simonw/archive/2007/01/17/622032.html

            扯淡

            metatable只是一個普通的table,當你它他當做metatable來用的時候,他就成了metatable:
               setmetatable( theFirstTable, theOtherTable )

            如果一個table有一個metatable,碰巧的是這個metatable有一寫特殊的關鍵字,則在使用這個table的時候,會發生一個寫有趣的事情:
             function gettable_event (table, key)
               local h
               if type(table) == "table" then
                 local v = rawget(table, key)
                 if v ~= nil then return v end
                 h = metatable(table).__index
                 if h == nil then return nil end
               else
                 h = metatable(table).__index
                 if h == nil then
                   error("...");
                 end
               end
               if type(h) == "function" then
                 return h(table, key)      -- call the handler
               else return h[key]          -- or repeat operation on it
            end

                也就是,你訪問表,其實最終訪問到表的metatable上去了。這些就是lua mirror a cplusplus class的基本原理。細節是復雜的,也很晦澀。


            Metatables

            15個重載方法(http://www.lua.org/manual/5.1/manual.html#2.8)

            We call the keys in a metatable events and the values metamethods. In the previous example, the event is "add" and the metamethod is the function that performs the addition.

            1. "add": the + operation.
            2. "sub": the - operation. Behavior similar to the "add" operation.
            3. "mul": the * operation. Behavior similar to the "add" operation.
            4. "div": the / operation. Behavior similar to the "add" operation.
            5. "mod": the % operation. Behavior similar to the "add" operation, with the operation o1 - floor(o1/o2)*o2 as the primitive operation.
            6. "pow": the ^ (exponentiation) operation. Behavior similar to the "add" operation, with the function pow (from the C math library) as the primitive operation."unm": the unary - operation.
            7. "concat": the .. (concatenation) operation.
            8. "len": the # operation.
            9. "eq": the == operation. The function getcomphandler defines how Lua chooses a metamethod for comparison operators. A metamethod only is selected when both
            10. objects being compared have the same type and the same metamethod for the selected operation.
            11. "lt": the < operation.
            12. "le": the <= operation.
            13. "index": The indexing access table[key].
            14. "newindex": The indexing assignment table[key] = value.
            15. "call": called when Lua calls a value.

            posted on 2011-07-02 20:49 的筆記 閱讀(298) 評論(0)  編輯 收藏 引用

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