Why declare local versions of functions?

[Pindrought]

I've been looking at source code for some existing addons, and I noticed something that doesn't make sense to me.


Why do they do this for all their functions?

local _G = _G
local abs = abs
local assert = assert
local collectgarbage = collectgarbage
local date = date

[myrroddin]

If the addon uses or calls those functions a lot, like in a loop that runs hundreds or thousands of times, or if the functions are tied to event handlers that fire all the time, then creating local references will trade RAM/memory for CPU efficiency.

-- psuedocode example
local n = 1
do
    print("The value of n is: ", n)
    n = n + 1
until n == 100000

print will be called 100,000 times, each one a lookup on the global table. That is not efficient.

local print = print -- looked up once, and kept in memory
local n = 1
do
    print("The value of n is: ", n)
    n = n + 1
until n == 100000

[Pindrought]

Originally Posted by myrroddin If the addon uses or calls those functions a lot, like in a loop that runs hundreds or thousands of times, or if the functions are tied to event handlers that fire all the time, then creating local references will trade RAM/memory for CPU efficiency. -- psuedocode example local n = 1 do     print("The value of n is: ", n) until n == 100000 print will be called 100,000 times, each one a lookup on the global table. That is not efficient. local print = print -- looked up once, and kept in memory local n = 1 do     print("The value of n is: ", n) until n == 100000

Such a good explanation! Thank you!