View source for WoW:Using the argument '...' efficiently

{{merge|Function arguments}}
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With patch 2.0 and the upgrade to lua 5.1, the '...' arg is much more powerful and less memory intensive than it was previously.  here's some handy tips on how to use this new functionality

== Hooking ==
Previously, the ... arg would create a table 'args' if called.  This allocated a table into memory, and thus became a source of garbage churn.  A very common pitfall of this came from hooking:
 local f = somefunc
 somefunc = function(...)
   -- do some crap
   return f(unpack(args))
 end
Now if this function is called often, or there are many hooks like this, there will be a significant hit on performance.  With lua 5.1 we can do this hook with no memory wasted
 local f = somefunc
 somefunc = function(...)
   -- do some crap
   return f(...)
 end

=== Post-hooks ===
The new functionality also allows for a nice clean post hook to be made.  In this example we need the first arg passed to the function, and we wish to maintain a full proper hook.  That means every arg is passed to the hooked function, and every return from that is returned back from our function.
 local f = somefunc
 local ph = function(a1, ...)
   -- do something with a1
   return ...
 end
 somefunc = function(a1, ...)
   return ph(a1, f(a1, ...)
 end

== Iterations ==
As with hooking, iteration over arbitrary number of args would create a table and thus waste memory.  With lua 5.1 we can do this cleanly in a for loop
 function f(...)
   for i=1,select("#", ...) do
     local x = select(i, ...)
     -- do something with x
   end
 end

== Recursion ==
Clean recursive functions are simple with ...
 function r(x, ...)
   local y = x*x
   if select("#", ...) > 0 then
     return y, r(...)
   else
     return y
   end
 end

[[Category:HOWTOs|U]]