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

464 Part III ■ Advanced Addon Techniqueswithout becoming tainted; and because that code can remain secure, it cancompile the attribute contents into an executable function that is also secure.When it compiles this function, it can also restrict its access to specific functionsand variables so that the secure function can’t use information that the Blizzarddesigners don’t want influencing sensitive decisions.Writing a SnippetA snippet is the body of a function, without the function (args, ...) andfinal end tags. These elements are provided by the secure code that compilesthe snippet into a usable function. Because many snippets emulate frame scripthandlers (OnClick, OnShow, and so on), the argument list is generally the sameas it would be in the equivalent XML script , , and so forth.Snippets often contain code comprised of quotes, line breaks, and othercharacters that normally need to be escaped inside Lua string literals. Becauseof this, there is an emerging convention to enclose snippet literals in [[longbrackets,]] which ignore all special characters (except the end of the bracket).This has the advantage of allowing you to format your code in a more naturalfashion, as well as often making it easier for you to distinguish the secure andinsecure parts of your addon code.You can demo a very simple snippet with the following line:/run SecureHandlerExecute(PlayerFrame, [[self:Hide()]])By itself, this isn’t terribly exciting. Insecure code can’t use SecureHandlerExecute during combat, and that code could always hide the player framedirectly. SecureHandlerExecute is mostly used to perform setup on more complexsecure handler frames. The real power of snippets and secure executioncomes from the ability to attach snippets to frames that will run them securelyin response to user input or selected state changes. Before we move on to that,though, put the player frame back by running the following code (snippetscan be stored in variables as well as in string literals):local showAction = [[self:Show()]]; iSecureHandlerExecute(PlayerFrame, showAction)Secure Handler FramesTo get WoW to compile and run your snippets, you have to store and attachthem correctly. The most common mechanism for this is a set of protectedtemplates called the secure handlers.Much the same way as SecureActionButtonTemplate provides a securefunction as its OnClick handler, these templates each provide one or twosecure functions as various script handlers. Each of these functions looks for