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用preload加載Lua導出模塊

用preload加載Lua導出模塊

(金慶的專欄 2017.5)

參考：
How to make exported module non-global?
https://github.com/SteveKChiu/lua-intf/issues/135

動態庫可以這樣導出模塊：

    extern "C"
    #if defined(_MSC_VER) || defined(__BORLANDC__) || defined(__CODEGEARC__)
    __declspec(dllexport)
    #endif
    int luaopen_modname(lua_State* L)
    {
        LuaRef mod = LuaRef::createTable(L);
        LuaBinding(mod)
            ...;
        mod.pushToStack();
        return 1;
    }

如果不是動態庫，可以這樣導出全局模塊 c_util：

int main()
{
   ...
   LuaBinding(L).beginModule("c_util")
       .addFunction("foo", []() { return 123; })
   .endModule();
   ...
}

如果不想讓它成為全局模塊，則需要在 package.preload 表中注冊一個加載函數.

Lua程序設計第3版英文版 programming in lua 3ed

The preload searcher allows the definition of an arbitrary function to load a module.
It uses a table, called package.preload, to map module names to loader functions.
When searching for a module name, this searcher simply looks for the given name in the table.
If it finds a function there, it returns this function as the module loader.
Otherwise, it returns nil.
This searcher provides a generic method to handle some non-conventional situations.
For instance, a C library statically linked to Lua can register its luaopen_ function into the preload table,
so that it will be called only when (and if) the user requires that module.
In this way, the program does not waste time opening the module if it is not used.

代碼示例：

    extern "C" int open_my_module(lua_State* L)
    {
        LuaRef mod = LuaRef::createTable(L);
        LuaBinding(mod)
            .addFunction("get_my_svr_id", &Util::GetMySvrId)
            ;
        mod.pushToStack();
        return 1;
    }

   int main()
   {
       ...
       LuaRef table(L, "package.preload");
       table["c_util"] = LuaRef::createFunctionWith(L, open_my_module);
       ...
   }

Lua 測試：
   assert(c_util == nil)
   local t = require("c_util")
   assert("table" == type(t))
   assert("function" == type(t.get_my_svr_id))

posted on 2017-05-10 16:11 金慶閱讀(749) 評論(0) 編輯收藏引用所屬分類: 1. C/C++

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