Memoize Function

ModuleScripts/Memoize.lua

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+--[[
+	memoize creates a function as a wrapper that caches the last outputs of a function.
+	This is useful if you know that the function should return the same output every
+	time it is run with the same inputs. The function should only return an output, and
+	not have any side effects. These side effects are not cached.
+
+	Without memoize's caching, even though the function ouputs the same values, the
+	memory locations of the values are different; tables made in the function, even if
+	they have the same values, won't be the same tables.
+
+	memoize only caches the last set of inputs and ouputs. This means that it is only
+	helpful when the function is likely to be called with the same inputs multiple
+	times in a row. This is the case with most Roact use cases.
+
+	Note that memoize only does a   ** shallow check on table inputs **   . This means
+	that if the same table is input but the elements of the table are different then
+	it will be assumed that the table has not changed.
+
+	In addition to all the previous warnings, memoize strips trailing nils. This means
+	that if foo is a memoized function and we call foo(), then foo(nil) will return a
+	cached value. This is opposed to how print handles input. print() only outputs a
+	new line, but print(nil) outputs "nil". This is because varargs can detect the
+	number of arguments passed in. So, be careful when using memoize with varargs.
+	Trailing nils will be stripped.
+
+	The wrapper can take any number of inputs and give any number of outputs.
+	Leading and interspersed nils are handled gracefully. Trailing nils on the input
+	are stripped.
+]]
+local function captureSize(...)
+	return {...}, select("#", ...)
+end
+
+local function memoize(func)
+	assert(type(func) == "function", "memoize requires a function to memoize")
+
+	local lastArgs
+	local lastNumArgs
+	local lastOutput
+	local lastNumOutput
+
+	return function(...)
+		local numArgs = select("#", ...)
+
+		while numArgs > 0 and select(numArgs, ...) == nil do
+			numArgs = numArgs - 1
+		end
+
+		if numArgs ~= lastNumArgs then
+			lastArgs = {...}
+			lastNumArgs = numArgs
+			lastOutput, lastNumOutput = captureSize(func(...))
+			return unpack(lastOutput, 1, lastNumOutput)
+		end
+
+		for i = 1, lastNumArgs do
+			if select(i, ...) ~= lastArgs[i] then
+				lastArgs = {...}
+				lastOutput, lastNumOutput = captureSize(func(...))
+				break
+			end
+		end
+
+		return unpack(lastOutput, 1, lastNumOutput)
+	end
+end
+
+return memoize