用户自定义类型

userdata：

userdata机制可让咱们在lua中使用c中的自定义数据类型。userdata表示一块动态分配的内存，这块内存就存储的自定义类型的数据，在lua脚本中使用userdata，并配合c提供的函数，就能够操做userdata了。

 

定义一个player类型：

typedef struct _Player {
    int id; 
    char name[20];
    int account;
} Player;

定义player的全部操做：

static int _index = 1;
static int player_new (lua_State* L) {
    const char* name = luaL_checkstring(L, 1);
    int len = strlen(name);

    Player* player = (Player*)lua_newuserdata(L, sizeof(Player)); // 使用lua_newuserdata建立userdata，并将其入栈
    player->id = _index++;
    memcpy(player->name, name, len + 1); // 须要拷贝一份字符串，不然栈在弹出的时候，字符串会被销毁
    player->account = 0;
    
    return 1;
}
static int player_print (lua_State* L) {
    Player* player = (Player*)lua_touserdata(L, 1);
    
    printf("player data: %d %s acount:%d \n", player->id, player->name, player->account);
    
    return 0;
}
static int player_charge (lua_State* L) {
    Player* player = (Player*)lua_touserdata(L, 1);
    int add = luaL_checkint(L, 2);
    
    player->account += add;
    
    return 0;
}

lua代码：

local player = Player.new("xiaoming")
local player1 = Player.new("xiaoqiang")

Player.charge(player1, 20)
Player.charge(player, 101)
Player.print(player)
Player.print(player1)

 

元表：

1. 相同的元表表明相同的类型，所以，咱们也使用元表来为userdata标示类型：

为userdata设置元表：

const char* CLASS_NAME_PLAYER = "Player_Class";

Player* player = lua_newuserdata(L, sizeof(Player));

lua_newmetatable(L, CLASS_NAME_PLAYER); // 建立一个新的元表，名字为player_class，并入栈

lua_setmetatable(L, -2); // 为位置在－2的userdata，设置元表，元表出栈

如何使用元表来进行类型判断：

将

Player* player = (Player*)lua_touserdata(L, 1);

改成

Player* player = (Player*)lua_checkudata(L, 1, CLASS_NAME_PLAYER); 若是userdata的类型不匹配，将抛出错误

2. 在lua中，元表除了能够标示类型，更重要的是模拟面向对象，和普通lua对象同样，userdata一样可使用元表机制来模拟面向对象：

咱们首先建立一个元表，只须要把对象的方法放在元表上，最重要的是设置元表的__index元方法：

luaL_newmetatable(L, CLASS_NAME_PLAYER); // 建立一个新的元表，并入栈，该元表是存放在全局做用域中的

...... // 设置一些对象方法

lua_pushvalue(L, -1); // 复制元表

lua_setfield(L, -2, "__index"); // 将元表的__index元方法设置为本身

在建立新对象的时候，只须要将新对象的元表设置为已经建立好的元表：

luaL_getmetatable(L, CLASS_NAME_PLAYER); // 将元表入栈

lua_setmetatable(L, -2); // 设置元表，元表出栈

上面的例子改成：

c代码：

static int _index = 1;
const char* CLASS_NAME_PLAYER = "PLAYER_CLASS";
static int player_new (lua_State* L) {
    dump(L);
    
    const char* name = luaL_checkstring(L, 1);
    int len = strlen(name);
    
    dump(L);
    
    Player* player = (Player*)lua_newuserdata(L, sizeof(Player));
    dump(L);
    player->id = _index++;
    memcpy(player->name, name, len + 1);
    player->account = 0;
    
　　// 使用已经建立好的元表
    luaL_getmetatable(L, CLASS_NAME_PLAYER);
    lua_setmetatable(L, -2);
    
    return 1;
}
static int player_print (lua_State* L) {
    Player* player = (Player*)luaL_checkudata(L, 1, CLASS_NAME_PLAYER);
    
    printf("player data: %d %s acount:%d \n", player->id, player->name, player->account);
    
    return 0;
}
static int player_charge (lua_State* L) {
    Player* player = (Player*)luaL_checkudata(L, 1, CLASS_NAME_PLAYER);
    int add = luaL_checkint(L, 2);
    
    player->account += add;
    
    return 0;
}
int libopen_player (lua_State* L) {
　　// 建立元表
    luaL_newmetatable(L, CLASS_NAME_PLAYER);
    lua_pushcfunction(L, player_print);
    lua_setfield(L, -2, "print");
    lua_pushcfunction(L, player_charge);
    lua_setfield(L, -2, "charge");
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    lua_settop(L, 0);
    
　　// 模块只有一个new方法了
    lua_newtable(L);
    lua_pushcfunction(L, player_new);
    lua_setfield(L, -2, "new");
    lua_setglobal(L, "Player");
    
    return 1;
}

lua代码：

local player = Player.new("xiaoming")
local player1 = Player.new("xiaoqiang")

player1:charge(30)
player:charge(20)
player:print()
player1:print();

 

轻量级的userdata：

对比彻底的userdta，轻量级的userdata只是c对象的一个指针，没有元表，就是一个普通的lua对象，就像number同样，所以轻量级的userdata不受lua垃圾回收机制的控制，必须本身管理内存。

c代码：

Player* player = nullptr;
static int player_pointer (lua_State* L) {
    player = new Player();
    player->id = 12;
    memcpy(player->name, "wulin", 6);
    player->account = 0;
    
    lua_pushlightuserdata(L, player);
    
    return 1;
}

lua代码：

local player1 = Player.pointer();
local player2 = Player.pointer();

print(player1);
print(player2);

 

userdata的内存回收：

userdata属于lua的内存管理机制，所以无须关系userdata的内存问题，但若是userdata使用了一些c内存中的对象，而且须要在userdata被删除的时候，同时删除这些对象，那么lua的内存回收机制就无能力为。这种状况下，lua为咱们提供了一个__gc元方法（只针对userdata），当userdata被删除时，会调用这个元方法，并将userdata做为参数传入，这样咱们就能够删除userdata中引用的c对象了。

在player中添加一个__gc的元方法：

static int player_delete (lua_State* L) {
    Player* player = (Player*)luaL_checkudata(L, 1, CLASS_NAME_PLAYER);
    
    printf("delete something not in lua memory... player name:%s \n", player->name);
    
    return 0;
}

int libopen_player (lua_State* L) {
    luaL_newmetatable(L, CLASS_NAME_PLAYER);
    lua_pushcfunction(L, player_print);
    lua_setfield(L, -2, "print");
    lua_pushcfunction(L, player_charge);
    lua_setfield(L, -2, "charge");
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    lua_pushcfunction(L, player_delete);
    lua_setfield(L, -2, "__gc"); // 添加__gc元方法
    lua_settop(L, 0);
    
    lua_newtable(L);
    lua_pushcfunction(L, player_new);
    lua_setfield(L, -2, "new");
    lua_pushcfunction(L, player_pointer);
    lua_setfield(L, -2, "pointer");
    lua_setglobal(L, "Player");
    
    return 1;
}

lua代码：

local player = Player.new("xiaoming")
player:charge(20)
player:print()

player = nil

collectgarbage(); // 强制进行垃圾回收