Re: Infinity as index
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- Subject: Re: Infinity as index
- From: "Lukas Prokop" <admin@...>
- Date: 2014年4月23日 19:56:19 +0200 (CEST)
> 2014年04月23日 11:53 GMT+02:00 Lukas Prokop <admin@lukas-prokop.at>:
>> Now my point is that we can use this as indices.
>
> I misunderstood your point. You mean indices for the string library,
> not indexing in a table. In that case, indices are converted to integers.
>
> The Lua value must be an integer, or a number or string convertible
> to an integer (see §3.4.3); otherwise, lua_tointegerx returns 0.
>
> Since infinity is not an integer, it is treated as 0.
Okay, thank you. So coming to the root of the problem, I guess there are 2
questions related to the same topic (which are partially answered by the
spec):
1. Shall inf, -inf and -nan be allowed as indices for strings?
2. Shall inf, -inf and -nan be numbers in general?
[leading to a change in semantics of lua_tointegerx]
Why shall we discuss it? Because this is non-intuitive for me:
> a = "hello world"
> inf = 1/0
> = a:sub(inf)
hello world
> = a:find("e", inf)
2 2
I have to point out that languages like python do not support infinity as
indices as well. Any other pros/cons?
best regards,
meisterluk