Lua 5.3.4 里的 ltm.c
我要先记录下在 ltm.h
的定义。这里面最重要就是 TMS
的定义了。
#ifndef ltm_h
#define ltm_h
#include "lobject.h"
/*
* WARNING: if you change the order of this enumeration,
* grep "ORDER TM" and "ORDER OP"
*/
typedef enum {
TM_INDEX,
TM_NEWINDEX,
TM_GC,
TM_MODE,
TM_LEN,
TM_EQ, /* last tag method with fast access */
TM_ADD,
TM_SUB,
TM_MUL,
TM_MOD,
TM_POW,
TM_DIV,
TM_IDIV,
TM_BAND,
TM_BOR,
TM_BXOR,
TM_SHL,
TM_SHR,
TM_UNM,
TM_BNOT,
TM_LT,
TM_LE,
TM_CONCAT,
TM_CALL,
TM_N /* number of elements in the enum */
} TMS;
#define gfasttm(g,et,e) ((et) == NULL ? NULL : \
((et)->flags & (1u<<(e))) ? NULL : luaT_gettm(et, e, (g)->tmname[e]))
#define fasttm(l,et,e) gfasttm(G(l), et, e)
#define ttypename(x) luaT_typenames_[(x) + 1]
LUAI_DDEC const char *const luaT_typenames_[LUA_TOTALTAGS];
LUAI_FUNC const char *luaT_objtypename (lua_State *L, const TValue *o);
LUAI_FUNC const TValue *luaT_gettm (Table *events, TMS event, TString *ename);
LUAI_FUNC const TValue *luaT_gettmbyobj (lua_State *L, const TValue *o,
TMS event);
LUAI_FUNC void luaT_init (lua_State *L);
LUAI_FUNC void luaT_callTM (lua_State *L, const TValue *f, const TValue *p1,
const TValue *p2, TValue *p3, int hasres);
LUAI_FUNC int luaT_callbinTM (lua_State *L, const TValue *p1, const TValue *p2,
StkId res, TMS event);
LUAI_FUNC void luaT_trybinTM (lua_State *L, const TValue *p1, const TValue *p2,
StkId res, TMS event);
LUAI_FUNC int luaT_callorderTM (lua_State *L, const TValue *p1,
const TValue *p2, TMS event);
#endif
luaT_objtypename
方法搜索 metatable
里面有没有 __name
的属性,有点话返回该属性,否则返回本身的类型名。我搜了一下,只在 ldebug.c
里面用到。
/*
** Return the name of the type of an object. For tables and userdata
** with metatable, use their '__name' metafield, if present.
*/
const char *luaT_objtypename (lua_State *L, const TValue *o) {
Table *mt;
if ((ttistable(o) && (mt = hvalue(o)->metatable) != NULL) ||
(ttisfulluserdata(o) && (mt = uvalue(o)->metatable) != NULL)) {
const TValue *name = luaH_getshortstr(mt, luaS_new(L, "__name"));
if (ttisstring(name)) /* is '__name' a string? */
return getstr(tsvalue(name)); /* use it as type name */
}
return ttypename(ttnov(o)); /* else use standard type name */
}
luaT_gettm
主要是给 gfasttm
和 fasttm
用到。
#define gfasttm(g,et,e) ((et) == NULL ? NULL : \
((et)->flags & (1u<<(e))) ? NULL : luaT_gettm(et, e, (g)->tmname[e]))
#define fasttm(l,et,e) gfasttm(G(l), et, e)
/*
** function to be used with macro "fasttm": optimized for absence of
** tag methods
*/
const TValue *luaT_gettm (Table *events, TMS event, TString *ename) {
const TValue *tm = luaH_getshortstr(events, ename);
lua_assert(event <= TM_EQ);
if (ttisnil(tm)) { /* no tag method? */
events->flags |= cast_byte(1u<<event); /* cache this fact */
return NULL;
}
else return tm;
}
luaT_gettmbyobj
返回 tag method。
const TValue *luaT_gettmbyobj (lua_State *L, const TValue *o, TMS event) {
Table *mt;
switch (ttnov(o)) {
case LUA_TTABLE:
mt = hvalue(o)->metatable;
break;
case LUA_TUSERDATA:
mt = uvalue(o)->metatable;
break;
default:
mt = G(L)->mt[ttnov(o)];
}
return (mt ? luaH_getshortstr(mt, G(L)->tmname[event]) : luaO_nilobject);
}
luaT_init
初始化 G(L)->tmname
。
void luaT_init (lua_State *L) {
static const char *const luaT_eventname[] = { /* ORDER TM */
"__index", "__newindex",
"__gc", "__mode", "__len", "__eq",
"__add", "__sub", "__mul", "__mod", "__pow",
"__div", "__idiv",
"__band", "__bor", "__bxor", "__shl", "__shr",
"__unm", "__bnot", "__lt", "__le",
"__concat", "__call"
};
int i;
for (i=0; i<TM_N; i++) {
G(L)->tmname[i] = luaS_new(L, luaT_eventname[i]);
luaC_fix(L, obj2gco(G(L)->tmname[i])); /* never collect these names */
}
}
luaT_callTM
调用 onst TValue *f
这个方法,传进来应该是一个 tm。这里面 stack 相关只能猜个大概。
void luaT_callTM (lua_State *L, const TValue *f, const TValue *p1,
const TValue *p2, TValue *p3, int hasres) {
ptrdiff_t result = savestack(L, p3);
StkId func = L->top;
setobj2s(L, func, f); /* push function (assume EXTRA_STACK) */
setobj2s(L, func + 1, p1); /* 1st argument */
setobj2s(L, func + 2, p2); /* 2nd argument */
L->top += 3;
if (!hasres) /* no result? 'p3' is third argument */
setobj2s(L, L->top++, p3); /* 3rd argument */
/* metamethod may yield only when called from Lua code */
if (isLua(L->ci))
luaD_call(L, func, hasres);
else
luaD_callnoyield(L, func, hasres);
if (hasres) { /* if has result, move it to its place */
p3 = restorestack(L, result);
setobjs2s(L, p3, --L->top);
}
}
luaT_callbinTM
跟 luaT_trybinTM
调用 binary 的 tm。
int luaT_callbinTM (lua_State *L, const TValue *p1, const TValue *p2,
StkId res, TMS event) {
const TValue *tm = luaT_gettmbyobj(L, p1, event); /* try first operand */
if (ttisnil(tm))
tm = luaT_gettmbyobj(L, p2, event); /* try second operand */
if (ttisnil(tm)) return 0;
luaT_callTM(L, tm, p1, p2, res, 1);
return 1;
}
void luaT_trybinTM (lua_State *L, const TValue *p1, const TValue *p2,
StkId res, TMS event) {
if (!luaT_callbinTM(L, p1, p2, res, event)) {
switch (event) {
case TM_CONCAT:
luaG_concaterror(L, p1, p2);
/* call never returns, but to avoid warnings: *//* FALLTHROUGH */
case TM_BAND: case TM_BOR: case TM_BXOR:
case TM_SHL: case TM_SHR: case TM_BNOT: {
lua_Number dummy;
if (tonumber(p1, &dummy) && tonumber(p2, &dummy))
luaG_tointerror(L, p1, p2);
else
luaG_opinterror(L, p1, p2, "perform bitwise operation on");
}
/* calls never return, but to avoid warnings: *//* FALLTHROUGH */
default:
luaG_opinterror(L, p1, p2, "perform arithmetic on");
}
}
}
luaT_callorderTM
可以在比较两个 table 的时候使用。
int luaT_callorderTM (lua_State *L, const TValue *p1, const TValue *p2,
TMS event) {
if (!luaT_callbinTM(L, p1, p2, L->top, event))
return -1; /* no metamethod */
else
return !l_isfalse(L->top);
}