WoW:API getn: Difference between revisions

WoW:API getn (source)

Revision as of 00:18, 31 July 2008

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    > print( #{1,2,3} )
+However, it does not always behave as one might expect. Consider the following sequence:
+ > t = { 1, 2, 3 }
+ > dump (#t)
-getn and the # operator start at index [1] and count up, ceasing when they reach a nil value. This means that if you have a table
+ > t[1] = nil
+ > dump (#t)
-  t = { [0]      = "zero",   --will not be counted
+  > dump (t)
-       [1]      = "one",    --will be counted; 1
+ {
-       [2]      = "two",    --will be counted; 2
+   [2] = 2
-       [3]      = "three",  --will be counted; 3
+  [3] = 3
-       ["four"] = "four",   --will not be counted; returns 3
+ } -- table: 0x807ff70
-       [5]      = "five" }  --will never be reached
-running getn(t) or #t will return 3, not the expected 4. Although there are 4 indices, it will count to three, see that t[4] is a blank spot, and return with a count of three. It will never reach 5. Furthermore, keys such as t["four"] and array values less than 1 such as t[0] are not counted at all.
+ > dump (#{ [2] = 2, [3] = 3 })
+As you can see, the # operator is unpredictable in that it can return different values for tables with identical contents. The Lua 5.1 reference manual has this to say about it [http://www.lua.org/manual/5.1/]:
+ The length of a table t is defined to be any integer index such that t[n] is not nil and t[n+1] is nil.
+In other words, be careful with this operator if you are using tables with holes in them. If your table has all its values between [1] and [n] for some n, with no nils in that range, the # operator will return n. Otherwise its result may be unclear.
 == See Also ==