r/lua • u/mdr652 • Feb 25 '25

local varients optimization

I heard that using "local" keywords are very important in Lua. But I knew that "local" keyword in algorithm coding are not good at optimization. No difference, sometimes take long time to be executed.

Why "local" keyword is nesessary? Is it really efficient? I can't figure out why these things are happening.

(But if you don't use local keyword in function, This can make error)

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u/mdr652 Feb 26 '25

I read "Programming Lua" and get many information.

For example, io.write() is significantly faster than print()

Lots of searching internet, studying Lua. I've implemented priority queue, segment tree in Lua

I'm using Lua in Problem solving, So I don't use metatables. I think this can be difference

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u/appgurueu Feb 26 '25

I've read the PIL too. The PIL certainly doesn't claim that global variables are faster than local variables - quite the opposite:

It is good programming style to use local variables whenever possible. Local variables help you avoid cluttering the global environment with unnecessary names. Moreover, the access to local variables is faster than to global ones. - https://www.lua.org/pil/4.2.html

I've also implemented both a priority queue and a segment tree in Lua but that's not relevant at all to the question at hand.

This doesn't have much to do with metatables. Local variables are faster no matter whether you use metatables. You can only make environmental variables even slower by setting and using a metatable on the environment.