Infinity as index
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- Subject: Infinity as index
- From: "Lukas Prokop" <admin@...>
- Date: 2014年4月23日 11:53:22 +0200 (CEST)
Hi,
I don't know whether this was thought through in any way, but lua defines
+inf and -inf as well as not-a-number.
Lua 5.2.3 Copyright (C) 1994-2013 Lua.org, PUC-Rio
> return math.huge
inf
> return 1/0
inf
> return 0/0
-nan
Of course, we can negate it as well (except for nan)
> return -math.huge
-inf
> return -1/0
-inf
> return -0/0
-nan
Now my point is that we can use this as indices. My intuition tells me the
following:
-nan - behaves like a nil as index or throws error (number expected)
inf - behaves like the end of a sequence as index
-inf - behaves like the beginning of a sequence as index
I guess -inf and nan behave as expected, because of checks like
if (init < 1) init = 1;
in lstrlib.c, but inf does not:
> return string.find("asd", "a", 1/0)
1 1
Thus, inf behaves like "nil" or "0". This is against my intuition. What is
your opinion?
best regards,
meisterluk
[0] https://twitter.com/meisterluk/status/457946586778464257
[1] A patch has to provided somewhere between lstrlib.c in function
str_find_aux line 582 and lapi.c in function lua_tointegerx line 349.
Somehow I only received a "1" from optinteger for the infinity value. This
got me confused.