Fix various issues and cleanup whitespace #9
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- better explanation of the length operator
- no functions in table constructors
- spaces after { and before }
| list[2] = nil | ||
| list[3] = "item" | ||
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| print(#list) -- undefined result |
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This should say that it returns 1 rather than the expected 3.
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With a given Lua implementation. But the definition in the language is even worse. In Lua 5.1:
any integer index n such that t[n] is not nil and t[n+1] is nil
So it could be 1 or 3.
In Lua 5.2 it is even clearer:
Unless a __len metamethod is given, the length of a table t is only defined if the table is a sequence, that is, the set of its positive numeric keys is equal to {1..n} for some integer n
So the operator could return anything. Or crash your program, for that matter. Actually I expect some later Lua implementations to raise an error in that situation.
Anyway, my point is: you cannot rely on it being 3 but you cannot rely on it being 1 either.
EDIT: If you think this undefined stuff is theoretical, guess what this prints:
print(#{1, 2, nil, 3})
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That's true; maybe expand it as result depends on Lua implementation, then?
I admit, I only tested it in Lua 5.1.5 and Luajit 2.0.2 to confirm.
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Yes, it depends on the implementation. And it is not consistent even on Lua 5.1.5. As I said in my edit above, if you put the hole just one step further it doesn't give the same answer:
Lua 5.1.5 Copyright (C) 1994-2012 Lua.org, PUC-Rio
> list = {}
> list[1] = "item"
> list[2] = "item"
> list[3] = nil
> list[4] = "item"
> =#list
4
If you are interested in the "why" see the implementation. Hint: binary search.
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Thanks for the cleanup! Just the one note above. |
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It was very nice of catwell to provide a pull request with the applied fixes and I can not understand the hold up here. The return value of the length operator on a table which is not a sequence, and in the case of 5.2 does not have a __len metamethod, is not defined. |
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@aDevilInMe No hold up, I just have been very busy and haven't had a chance to merge. Will do so, after I fix the merge conflict, once I have time. |
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