concat number with string to convert it doesn't typecheck by default, but it's faster than tostring()

[matthargett]

benchmarking

local x = 5
x ..= ""

versus

local x = 5
x = tostring(x)

the ..= version is ~100us faster than tostring(), even though ..= doesn't typecheck and isn't as idiomatic.

[boatbomber]

Backing up that "faster" claim: (the 100us metric in OP was with N=10k, I've bumped it to 20k in the screenshot to show it more easily at a glance)

Using the following to test:

local N = 20_000
return {
	ParameterGenerator = function()
		local nums = table.create(N)
		for i=1, N do
			nums[i] = math.random(1, 10000000)
		end
		return nums
	end,

	Functions = {
		["concat"] = function(Profiler, nums)
			for _, num in nums do
				num ..= ""
			end
		end,

		["tostring"] = function(Profiler, nums)
			for _, num in nums do
				num = tostring(num)
			end
		end,

		["format"] = function(Profiler, nums)
			for _, num in nums do
				num = string.format("%f", num)
			end
		end,
	},
}

[zeux]

I think that's just a performance bug. We don't have a fastcall for tostring/tonumber - we absolutely can add that.