lua中的statement类别for

• for的构成一般由以下例子构成

    for i = 1, 10 do
    end
    for i = 1, 10, 2 do
    end

    for a,b in ipairs({}) do

    end
    for a,b in pairs({}) do

    end

static void forstat(LexState *ls, int line)
{


    varname = str_checkname(ls); // 第一个变量名
    switch (ls->t.token)
    {
    case '=':
        fornum(ls, varname, line);
        break;
    case ',':
    case TK_IN:
        forlist(ls, varname);
        break;
    }
    check_match(ls, TK_END, TK_FOR, line);
    leaveblock(fs); /* loop scope (`break' jumps to this point) */
}

    static void fornum(LexState *ls, TString *varname, int line)
{
    FuncState *fs = ls->fs;
    int base = fs->freereg;
    new_localvarliteral(ls, "(for index)", 0);
    new_localvarliteral(ls, "(for limit)", 1);
    new_localvarliteral(ls, "(for step)", 2);
    new_localvar(ls, varname, 3);
    checknext(ls, '=');
    exp1(ls); /* initial value */
    checknext(ls, ',');
    exp1(ls); /* limit */
    if (testnext(ls, ','))
        exp1(ls); /* optional step */
    else
    { /* default step = 1 */
        gafqK_codeABx(fs, OP_LOADK, fs->freereg, gafqK_numberK(fs, 1));
        gafqK_reserveregs(fs, 1);
    }
    forbody(ls, base, line, 1, 1);
}

• 注册一个新的local变量,会先检查local变量的数量,然后将变量放入proto的locvars中,然后返回 当前本地变量的数量

// 解析新的local变量
    static void new_localvar(LexState *ls, TString *name, int n)
    {
        FuncState *fs = ls->fs;
        gafqY_checklimit(fs, fs->nactvar + n + 1, GAFQI_MAXVARS, "local variables");
        fs->actvar[fs->nactvar + n] = cast(unsigned short, registerlocalvar(ls, name));
    }

    static int registerlocalvar(LexState *ls, TString *varname)
{
    FuncState *fs = ls->fs;
    Proto *f = fs->f;
    int oldsize = f->sizelocvars;
    gafqM_growvector(ls->L, f->locvars, fs->nlocvars, f->sizelocvars, LocVar, SHRT_MAX, "too many local variables");
    while (oldsize < f->sizelocvars)
        f->locvars[oldsize++].varname = NULL;
    f->locvars[fs->nlocvars].varname = varname;
    gafqC_objbarrier(ls->L, f, varname);
    return fs->nlocvars++;
}

static int exp1(LexState *ls)
{
    expdesc e;
    int k;
    expr(ls, &e);
    k = e.k;
    gafqK_exp2nextreg(ls->fs, &e);
    return k;
}

void gafqK_exp2nextreg(FuncState *fs, expdesc *e)
{
    gafqK_dischargevars(fs, e);
    freeexp(fs, e);
    gafqK_reserveregs(fs, 1);
    exp2reg(fs, e, fs->freereg - 1);
}

// 把表达式放进寄存器中
static void exp2reg(FuncState *fs, expdesc *e, int reg)
{
    discharge2reg(fs, e, reg);
    e->f = e->t = NO_JUMP;
    e->u.s.info = reg;
    e->k = VNONRELOC;
}

// reg是要被使用的寄存器的位置
static void discharge2reg(FuncState *fs, expdesc *e, int reg)
{
    gafqK_dischargevars(fs, e);
    switch (e->k)
    {
    case VKNUM:
    {
        gafqK_codeABx(fs, OP_LOADK, reg, gafqK_numberK(fs, e->u.nval)); // 这里生成一个操作指令, 把值存到常量k里面去
        break;
    }
    }
    e->u.s.info = reg;
    e->k = VNONRELOC;
}

// isnum 是否是数字类型的循环 for i = 1, 10 do
static void forbody(LexState *ls, int base, int line, int nvars, int isnum)
{

    checknext(ls, TK_DO);
    prep = isnum ? gafqK_codeAsBx(fs, OP_FORPREP, base, NO_JUMP) : gafqK_jump(fs);
    enterblock(fs, &bl, 0);
    adjustlocalvars(ls, nvars);
    gafqK_reserveregs(fs, nvars);
    block(ls);
    leaveblock(fs); /* end of scope for declared variables */
    gafqK_patchtohere(fs, prep);
    endfor = (isnum) ? gafqK_codeAsBx(fs, OP_FORLOOP, base, NO_JUMP) : gafqK_codeABC(fs, OP_TFORLOOP, base, 0, nvars);
    gafqK_fixline(fs, line); /* pretend that `OP_FOR' starts the loop */
    gafqK_patchlist(fs, (isnum ? endfor : gafqK_jump(fs)), prep + 1);
}