Advantages of local variables

[skittles sour]

Hi so Lua manuals say that local variables enjoy faster access. How much faster is this access? Besides this advantage, and the advantage of not cluttering the global environment, what other advantages does the local variable enjoy?

[CarlZalph]

For each variable reference, LUA will try to first find it in the local table, and if that fails then it looks to the environment table, and then if that fails to the global table.

Each lookup is effectively a hashmap lookup, so for a tight loop having things cached in local will be a good thing to do for performance.

a = 0
for i=0,100000
do
    a = a + math.sin(a)
end
--
local a = 0
local msin = math.sin
for i=0,100000
do
    a = a + msin(a)
end

The bottom one will be done quicker than the top due to the locality lookups.

 

In the case of mods it's good practice to keep variables that aren't to be used outside of the mod local.

Keeps the references in check for garbage collection (memory usage) and does less on the CPU for better performance.