Editing WoW:Lua variable scoping (section)

== Scope de-resolution ==
Sometimes it is necessary to use a global version of a variable instead of a local copy which may exist. Luckily, Lua provides a mechanism to do this. In general, it won't be necessary if you follow programming best-practices, but occasionally it can be useful to use. Lua provides two methods to obtain a global variable:
#The [[API_getglobal|getglobal]]() function
#The [[Dump_G|_G]] table

=== The [[API_getglobal|getglobal]]() function ===

''NOTE:'' AS OF PATCH 4.0.1 getlobal() is depreciated and won't work for WOW addons. Use the _G global table methods discussed in the next section. [Also applies to setglobal()]

A function provided by the Lua language is [[API_getglobal|getglobal]](). It does precisely what its name states -- it retrieves a global variable and returns it. To use this function, you pass in a string representation of its name:

   n = 1;                                         -- Global n
   local n = 2;                                   -- Local n
   DEFAULT_CHAT_FRAME:AddMessage(n);              -- Outputs 2
   DEFAULT_CHAT_FRAME:AddMessage(getglobal("n")); -- Outputs 1

Because getglobal() can be expensive, and in general it is easier to access local variables than global variables, often times, programmers will create local copies of globals they retrieve. This can make code much easier to understand and run:

   n = 1;                                         -- Global n
   local n = 2;                                   -- Local n
   local global_n = getglobal("n");               -- Make local copy of global
   DEFAULT_CHAT_FRAME:AddMessage(n);              -- Outputs 2
   DEFAULT_CHAT_FRAME:AddMessage(global_n);       -- Outputs 1

=== The _G Table ===
Lua also creates and maintains a table defined by the language which contains all global variables. This table is named _G. You access it similarly to getglobal() — its keys are the string representations of variable names. As such, the same block exemplified in the previous section could be rewritten thusly, with the exact same result:

   local global_n = getglobal("n");   -- These two lines
   local global_n = _G["n"];          -- are functionally equivalent

This can allow authors to write much more compact code which performs the same operation, though it may be less readable. As always, use the appropriate tool for the situation to help maintain readability.