小编Ada*_*dam的帖子

如何重新创建setfenvLua 5.2中的功能？我很难理解你应该如何使用新的_ENV环境变量.

在Lua 5.1中,您可以setfenv非常轻松地使用沙箱任何功能.

--# Lua 5.1

print('_G', _G)             -- address of _G

local foo = function()  
    print('env', _G)        -- address of sandbox _G
    bar = 1
end

-- create a simple sandbox
local env = { print = print }
env._G = env

-- set the environment and call the function
setfenv(foo, env)
foo()

-- we should have global in our environment table but not in _G
print(bar, env.bar)

运行此示例显示输出:

_G    table: 0x62d6b0 …

请考虑以下示例程序:

#include <stdio.h>

struct base {
    int a, b;
};

struct embedded {
    struct base base;
    int c, d;
};

struct pointed {
    struct base* base;
    int c, d;
};

static void base_print(struct base* x) {
    printf("a: %d, b: %d\n", x->a, x->b);
}

static void tobase_embedded(void* object) {
    base_print(object); // no cast needed, suitably converted into first member.
}

static void tobase_pointed(void* object) {
    struct base* x = *(struct base**) object; // need this cast?
    base_print(x);
}

int main(void) { …

我试图通过使用C API将其存储在弱表中来为函数值创建GC终结器.

我开始在纯Lua 5.2中编写原型:

local function myfinalizer()
   print 'Called finalizer'
end

function myfunc()
   print 'Called myfunc'
end

local sentinels = setmetatable({}, { __mode='k' })
sentinels[myfunc] = setmetatable({}, { __gc=myfinalizer })

myfunc()
myfunc = nil
collectgarbage 'collect'

print 'Closing Lua'

结果输出:

Called myfunc
Called finalizer
Closing Lua

原型似乎按预期工作.以下是C版:

#include <stdlib.h>
#include <stdio.h>
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"

static int my_finalizer(lua_State *L)
{
    puts("Called finalizer");
    return 0;
}

static int my_func(lua_State *L)
{
    puts("Called myfunc");
    return 0;
}

int main(void)
{ …

在Lua 5.3中,C API中的表相关函数接收和返回lua_Integer.

void lua_rawgeti (lua_State *L, int idx, lua_Integer n);
void lua_rawseti (lua_State *L, int idx, lua_Integer n);
lua_Integer luaL_len (lua_State *L, int index);

但是,lua_createtable仍然收到int.

void lua_createtable (lua_State *L, int narr, int nrec);

在下面的示例函数中,源表的长度用于创建大小相同的副本.

static int copy_sequence(lua_State *L) {
   lua_Integer len, i;
   luaL_checktype(L, 1, LUA_TTABLE);
   len = luaL_len(L, 1);
   lua_createtable(L, (int)len, 0); /* conversion warning */
   for (i = 1; i <= len; i++) {
      lua_rawgeti(L, 1, i);
      lua_rawseti(L, -2, i);
   }
   return …