|It has been suggested that this article or section be merged with Function arguments.|
*Please see the discussion page for reasoning.
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
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
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
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
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