Lua的数据对象表示

#define CommonHeader	GCObject *next; lu_byte tt; lu_byte marked
struct GCObject ｛
  CommonHeader;
｝;
typedef union Value ｛
  GCObject *gc;    /* collectable objects */
  void *p;         /* light userdata */
  int b;           /* booleans */
  lua_CFunction f; /* light C functions */
  lua_Integer i;   /* integer numbers */
  lua_Number n;    /* float numbers */
｝ Value;
#define TValuefields	Value value_; int tt_
typedef struct lua_TValue ｛
  TValuefields;
｝ TValue;
#define LUA_TNIL			0
#define LUA_TBOOLEAN		1
#define LUA_TLIGHTUSERDATA	2
#define LUA_TNUMBER			3
#define LUA_TSTRING			4
#define LUA_TTABLE			5
#define LUA_TFUNCTION		6
#define LUA_TUSERDATA		7
#define LUA_TTHREAD			8
数据对象由lua_TValue表示，分为两部分。
int tt_表示对象的类型；Value value_为具体值。
tt_的最后4bit表示对象的主类型，倒数5、6位表示子类型，7位表示是否可回收，其它位表示对象的tag
获取对象的值的过程：根据类型tt_从联合体value_中取出相应的值。
例：tt_为LUA_TNUMBER时，获取值分两种情况
    当tt_等于LUA_TNUMINT取value_的i（整型）
	当tt_等于LUA_TNUMFLT取value的n（浮点型）的值。
以下分九种类型分别描述lua的对象	
0、nil
obj = ｛value_ = ｛NULL｝,tt_ = LUA_TNIL｝
1、boolean
true = ｛value_ = ｛b=1｝,tt_ = LUA_TBOOLEAN｝
false= ｛value_ = ｛b=0｝,tt_ = LUA_TBOOLEAN｝
2、light userdata
pc表示C语言的指针
obj = ｛value_ = ｛p=pc｝,tt_ = LUA_TLIGHTUSERDATA｝
3、整数和浮点数
#define LUA_TNUMFLT	(LUA_TNUMBER | (0 << 4))  /* float numbers */
#define LUA_TNUMINT	(LUA_TNUMBER | (1 << 4))  /* integer numbers */
int_value为整数的值
float_value为浮点数的值
int_obj = ｛value_ = ｛i=int_value｝,tt_=LUA_TNUMINT｝
float_obj = ｛value_ = ｛n=float_value｝,tt_=LUA_TNUMFLT｝
4、string
lua_TValue对象并不直接存放string的字符串，gc指向TString ts
str = ｛value_ = ｛gc=ts｝,tt_ = LUA_TSTRING｝
string对象的真实结构
// Header for string value; string bytes follow the end of this structure
typedef struct TString ｛
  CommonHeader;
  lu_byte extra;  /* reserved words for short strings; "has hash" for longs */
  lu_byte shrlen;  /* length for short strings */
  unsigned int hash;
  union ｛
    size_t lnglen;  /* length for long strings */
    struct TString *hnext;  /* linked list for hash table */
  ｝ u;
｝ TString;
5、table
typedef union TKey ｛
  struct ｛
    TValuefields;
    int next;  /* for chaining (offset for next node) */
  ｝ nk;
  TValue tvk;
｝ TKey;
/* copy a value into a key without messing up field 'next' */
#define setnodekey(L,key,obj) \
	｛ TKey *k_=(key); const TValue *io_=(obj); \
	  k_->nk.value_ = io_->value_; k_->nk.tt_ = io_->tt_; \
	  (void)L; checkliveness(L,io_); ｝
typedef struct Node ｛
  TValue i_val;
  TKey i_key;
｝ Node;
typedef struct Table ｛
  CommonHeader;
  lu_byte flags;  /* 1<<p means tagmethod(p) is not present */
  lu_byte lsizenode;  /* log2 of size of 'node' array */
  unsigned int sizearray;  /* size of 'array' array */
  TValue *array;  /* array part */
  Node *node;
  Node *lastfree;  /* any free position is before this position */
  struct Table *metatable;
  GCObject *gclist;
｝ Table;
t指向Table的指针
lua_TValue obj = ｛value_ = ｛gc=t｝,tt_ = LUA_TTABLE｝
6、function
#define LUA_TLCL	(LUA_TFUNCTION | (0 << 4))  /* Lua closure */
#define LUA_TLCF	(LUA_TFUNCTION | (1 << 4))  /* light C function */
#define LUA_TCCL	(LUA_TFUNCTION | (2 << 4))  /* C closure */
#define ClosureHeader \
	CommonHeader; lu_byte nupvalues; GCObject *gclist
typedef struct CClosure ｛
  ClosureHeader;
  lua_CFunction f;
  TValue upvalue[1];  /* list of upvalues */
｝ CClosure;
typedef struct LClosure ｛
  ClosureHeader;
  struct Proto *p;
  UpVal *upvals[1];  /* list of upvalues */
｝ LClosure;
typedef union Closure ｛
  CClosure c;
  LClosure l;
｝ Closure;
lua closure
obj = ｛value_ = ｛gc=x｝,tt_ = LUA_TLCL｝
light C function
typedef int (*lua_CFunction) (lua_State *L);
obj = ｛value_ = ｛f=x｝,tt_ = LUA_TLCF｝
C closure
obj = ｛value_ = ｛gc=x｝,tt_ = LUA_TCCL｝
7、user data
typedef struct Udata ｛
  CommonHeader;
  lu_byte ttuv_;  /* user value's tag */
  struct Table *metatable;
  size_t len;  /* number of bytes */
  union Value user_;  /* user value */
｝ Udata;
obj = ｛value_ = ｛gc=x｝,tt_ = LUA_TUSERDATA｝
8、thread
x表示lua_State指针
obj = ｛value_ = ｛gc=x｝,tt_ = LUA_TTHREAD｝