WoW:API getn: Difference between revisions

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-{{:Lua/Libshortcut|getn|table.getn}}
+{{ambox
+|border=red
+|type='''Warning: This article discusses use of a deprecated function.'''
+|style=margin-right: 10em
+|info=*This function should no longer be used in Lua 5.1 and may be removed in the future.
+*Use of it will result in potential future incompatibility.}}{{luaapi}}
 From [http://lua-users.org/wiki/TableLibraryTutorial TableLibraryTutorial] of lua-users.org.
   table.getn(table)
+ getn(table)
-{{ambox
-|border=red
-|type='''Warning: This article discusses use of a deprecated function.'''
-|info=*This function should no longer be used in Lua 5.1 and may be removed in the future.
-*Use of it will result in potential future incompatibility.}}
 This is used to determine the size of a table. The size of a table is discussed at the top of this page.
@@ Line 26: / Line 27: @@
    > print( #{1,2,3} )
+However, it does not always behave as one might expect. Consider the following sequence:
+ > t = { 1, 2, 3 }
+ > dump (#t)
+ > t[1] = nil
+ > 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
+ > dump (t)
+ {
+  [2] = 2
+  [3] = 3
+ } -- table: 0x807ff70
-  t = { [0]      = "zero",   --will not be counted
+  > dump (#{ [2] = 2, [3] = 3 })
-       [1]      = "one",    --will be counted; 1
-       [2]      = "two",    --will be counted; 2
+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/]:
-       [3]      = "three",  --will be counted; 3
+ 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.
-       ["four"] = "four",   --will not be counted; returns 3
+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.
-       [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.
+Note:
+The reason the returned values are different is because the tables are different. For indexed tables, or tables that start with index values like 1,2,3 for keys, use tinsert and tremove to change the contents. What # returns is actually correct, setting the index value to nil does not change the size of the table for index keys, tremove would.
 == See Also ==
 * [[tcount]]
-{{LUA}}