Metatables

參考資料

Referenced Values, Metatables, and Simple Inheritance>

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