Wiley-World.of.Warcraft.Programming.A.Guide.and.Reference.for.Creating.WoW.Addons

542 Part IV ■ ReferenceAPI Meta-TypesTo clarify the documentation of API functions, we have created a number of meta-typesthat are used to describe what sort of values are accepted in an argument or returnedfrom an API function. These are not actual Lua types, but a classification of acceptedvalues in various API sub-systems. When a meta-type applies to an argument or returnvalue, this is indicated after the Lua type in the argument listing. Meta-types enableyou to consolidate the documentation for classes of API functions, rather than having todocument the same list of values over and over again. This section describes these types.1nilMany API functions use values indicative of a binary state but do not utilize theBoolean true and false values in Lua. Due to the way the functions are limited, theyuse the number value 1 for true,andnil for false. Because Lua treats nil as a falsevalue and any non-nil value as true in a conditional, these values can generally beused the same as Boolean values in conditional statements (such as if IsInGuild()then ... end). However, you should avoid making direct comparisons using thistype of value: for example, the condition if IsInGuild() == true then ... endwill never be triggered. These types of variables are called 1nil values, to distinguishthem from Boolean values.actionIDThe actionID meta-type is used to identify one of the player’s action bar slots. InUI terms, action bar slots are a layer of abstraction between spells or items and themechanisms available to the player for using them conveniently. For example, insteadof the default UI internally using SetBindingSpell(), SetBindingMacro(), andso on whenever the player changes the contents of the visible action bars, it insteadmanages a set of key bindings corresponding to the action bar slots.