Table.sort optimizations

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1

lets say i do

table.sort(t,function(a,b)
      return someExpensiveFunction(a)>someExpensiveFunction(b)
end)

That comparator function will almost certainly be ran multiple times with at least 1 of the same entries (uses some quicksort hybrid alg from the minimal research i did)

But does the compiler optimize for me and know to only call someExpensiveFunction once per entry and then cache it, or would there be multiple calls?

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2

No, the compiler would not cache it for you. There would be multiple calls. This is because it would call your function every time it needs to compare the two elements.

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3

As the previous person said, no, you have to do it:

local cache = {}
for _, v in pairs(t) do
	cache[v] = someExpensiveFunction(v)
end
table.sort(t, function(a, b)
	return cache[a] > cache[b]
end)
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