Re: [ANN] Lua 5.3.0 (beta) now available
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- Subject: Re: [ANN] Lua 5.3.0 (beta) now available
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2014年11月16日 12:07:14 -0200
> In lvm.h:
>
> #define tonumber(o,n) \
> (ttisfloat(o) ? (*(n) = fltvalue(o), 1) : luaV_tonumber_(o,n))
>
> Yet `luaV_tonumber_` already handles this case.
> We could probably get rid of the #define altogether and just use
> `luaV_tonumber_`.
>
> I'm also wondering why we gained the "_" suffix.
The define saves a function call in what we expect to be a common case
(using a float as a float). The suffix is a convention in Lua that a
function should not be called directly, only thourgh its corresponding
macro. The fact that luaV_tonumber_ handles floats is an implementation
detail, a consequence of its way of converting "integer strings" to
floats. It could as well be implemented like this:
int luaV_tonumber_ (const TValue *obj, lua_Number *n) {
TValue v;
if (ttisinteger(obj)) {
*n = cast_num(ivalue(obj));
return 1;
}
else if (cvt2num(obj) && /* string convertible to number? */
luaO_str2num(svalue(obj), &v) == tsvalue(obj)->len + 1) {
if (ttisinteger(&v))
*n = cast_num(ivalue(&v));
else
*n = fltvalue(&v);
return 1;
}
return 0; /* conversion failed */
}
-- Roberto