lua-5.1-alpha: length operator on tables (arrays) and nil values
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- Subject: lua-5.1-alpha: length operator on tables (arrays) and nil values
- From: Michael Roth <mroth@...>
- Date: 2005年9月13日 23:57:54 +0200
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Hello list,
I have a question regarding the new length operator.
The documentation of 5.1-alpha says:
The length of a table t is defined to be any integer
index n such that t[n] is not nil and t[n+1] is nil;
moreover, if t[1] is nil, n may be zero.
[...]
If the array has "holes" (that is, nil values between
other non-nil values), then #t may be any of the indices
that precede a nil value [...]
This is a problem, because it could result to weird results:
t = { 1, 2, 3, 4, 5, 6, 7, 8 }
t[5] = nil
t[8] = nil
#t ---> 7
But:
t = { 1, 2, 3, 4, 5, 6, 7, 8 }
t[4] = nil
t[8] = nil
#t ---> 3
And, more weird:
t = {}
t[1] = 1
t[4] = 4
#t ---> 1
t[2] = nil
t[3] = nil
#t ---> 4
So the problem arise, in 5.1-alpha there isn't a way to get the index of
the largest non nil value in an array. Even lua_objlen() doesn't help.
This will result in some more headache in vararg functions called with
nil arguments...
So, my question is: How to deal with this situation? How to use arrays
containing holes? How to handle nil arguments in vararg functions?
To me it looks like that in 5.1-alpha arrays are simple not able to
handle nil values. What's the rational behind this decision?
cu
Michael
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