Editing WoW:API TYPE Boolean

{{wowapitype}}
The special WoW 'boolean' API type, use in WoW Lua and the WoW API.

Typically a '''boolean''' data type is one that by definition only has two states, "true" and "false". The old WoW boolean Type is defined by number 1 and {{api|nil|t=t}}, for true and false. Many older APIs in WoW use these semantics for bool.

== History of Booleans in WoW ==

In [[Lua]], the programming language used by the World of Warcraft [[User Interface]], real booleans were not introduced until version 5.0.

Early versions of World of Warcraft used Lua v4, which shows in that the majority of [[API]]s still return '''1''' for "true", and '''nil''' for "false".

In Lua, there are only two values that evaluate to a boolean false: '''false''' and '''nil'''.

'''ALL OTHER VALUES EVALUATE TO TRUE'''. Including 0, which is an important distinction for e.g. {{wplink|C programming language|C/C++}} programmers.

== Gotchas with Boolean types in Lua ==
When used in '''if ... then''' clauses a '''1''' result is the same as a '''true''' result, so you do not have to worry there.
But beware of ''comparing'' the returns of supposedly-boolean functions with eachother without forcing them to actually be boolean.

Example:
 function Func1() return 1; end     -- old-style function returning 1 for true
 function Func2() return true; end  -- new-style function actually using true
 
 if(Func1() == Func2()) then
   print "They're both the same!";
 else
   print "They're different!";
 end

This would output '''"They're different!"''', because ''1 and true are not the same thing in Lua''.

You can force a value to be boolean by NOTing it twice, like so:
 definitelyBoolean = not not kindaBoolean;

In the earlier disfunctional example, we'd get away with NOTing it just once since we're only testing if they're the same:
 if( (not Func1()) == (not Func2()) ) then
   ...

== See Also ==
* [[API types]]
* [[XML types]]
* [[XML attribute types]]
[[Category:API types]]
[[Category:Glossary]]