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

1320 Part V ■ AppendixesEven if you do not know beforehand what conditions will be most likely,some simple profiling tests can help figure that out for you. For instance,you could maintain counters for each clause that increment whenever theyexecute. Then you could create a function to print out the stats. Most of thetime, such optimization is unnecessary. If you’re doing anything in OnUpdateor some other extremely frequent code path, though, it may just be worth theresearch. (Remember to remove said counters for the release version of yourmod because incrementing them has its own performance impact.)Exploit Shortcut EvaluationIn a similar vein, you can use a feature of Lua (and other programminglanguages) called shortcut evaluation to optimize the conditionals themselves.Consider the expression a or b.Theor operator evaluates to true if eithera or b evaluates to true. Once Lua knows that a is true, there is no reason toevaluate b. Similarly, as soon as it’s known that c is false in the expressionc and d, the entire expression is known to be false.This also has the interesting benefit (in Lua) that every non-nil, non-falsevalue is considered true. Then you can initialize in the following way:variable = variable or “Some default string“to accomplish something equivalent to the following:if not variable thenvariable = “Some default string“endDepending on your specific need, you may find the Boolean expressioneasier to read.In addition, any time you have a complex condition with several clauses,you should try to put the most likely and/or fastest-to-evaluate clauses first.In pseudo-code, this would look something like the following:if likely condition or less likely condition thendo stuffelseif fast condition and slow condition thendo stuffendNOTE This section describes the logical result of the evaluation of Booleanexpressions. As discussed in Chapter 2, the actual results of the and and oroperators are one of the two operands depending on whether the first one isinterpreted as true (anything other than false or nil)—thereturn table.remove(freeTables) or {} statement from the earlierGetTable function, for example.