feat: helper to memoize 2 parameter function

lua/spec/fn_util_spec.lua

@@ -26,6 +26,59 @@ describe('function utils', function()
 		end)
 	end)
 
+	describe('memoize2', function()
+		it('check', function()
+			local calledCount = 0
+			local multiply = FnUtil.memoize2(function(x, y)
+				calledCount = calledCount + 1
+				if x ~= nil and y ~= nil then
+					return x * y
+				end
+				if x == nil and y == nil then
+					return nil
+				end
+				return 0
+			end)
+
+			assert.are_equal(0, calledCount)
+			assert.are_equal(4, multiply(2, 2))
+			assert.are_equal(1, calledCount)
+			assert.are_equal(4, multiply(2, 2))
+			assert.are_equal(1, calledCount)
+			assert.are_equal(9, multiply(3, 3))
+			assert.are_equal(2, calledCount)
+			assert.are_equal(9, multiply(3, 3))
+			assert.are_equal(2, calledCount)
+			assert.is_nil(multiply(nil, nil))
+			assert.is_nil(multiply(nil, nil))
+			assert.is_nil(multiply(nil, nil))
+			assert.are_equal(3, calledCount)
+			-- Mixed nil inputs are memoized independently
+			assert.are_equal(0, multiply(2, nil))
+			assert.are_equal(4, calledCount)
+			assert.are_equal(0, multiply(2, nil))
+			assert.are_equal(4, calledCount)
+			assert.are_equal(0, multiply(nil, 3))
+			assert.are_equal(5, calledCount)
+			assert.are_equal(0, multiply(nil, 3))
+			assert.are_equal(5, calledCount)
+			-- Argument order produces separate cache entries
+			assert.are_equal(6, multiply(2, 3))
+			assert.are_equal(6, calledCount)
+			assert.are_equal(6, multiply(3, 2))
+			assert.are_equal(7, calledCount)
+			assert.are_equal(6, multiply(2, 3))
+			assert.are_equal(7, calledCount)
+			assert.are_equal(6, multiply(3, 2))
+			assert.are_equal(7, calledCount)
+			-- Previously computed values remain cached after new computations
+			assert.are_equal(4, multiply(2, 2))
+			assert.are_equal(7, calledCount)
+			assert.are_equal(9, multiply(3, 3))
+			assert.are_equal(7, calledCount)
+		end)
+	end)
+
 	describe('memoize Y', function()
 		it('check', function()
 			local calledCount = 0

lua/wikis/commons/FnUtil.lua

@@ -1,3 +1,3 @@
 ---
 -- @Liquipedia
 -- page=Module:FnUtil
@@ -11,6 +11,7 @@
 local FnUtil = {}
 
 ---@alias memoizableFunction fun(input: any): any
+---@alias memoizableFunction2 fun(input: any, input2: any): any
 
 ---Creates a memoized copy of a 0 or 1 param function.
 ---@generic T:memoizableFunction
@@ -38,6 +39,34 @@
 	end
 end
 
+---Creates a memoized copy of a 2 param function.
+---@generic T:memoizableFunction2
+---@param func T
+---@return T
+function FnUtil.memoize2(func)
+	local called = {}
+	local results = {}
+	local xNil = FnUtil.memoize(function(y) return func(nil, y) end)
+	local yNil = FnUtil.memoize(function(x) return func(x, nil) end)
+	return function(x, y)
+		if y == nil then
+			return yNil(x)
+		elseif x == nil then
+			return xNil(y)
+		else
+			if not called[x] then
+				called[x] = {}
+				results[x] = {}
+			end
+			if not called[x][y] then
+				called[x][y] = true
+				results[x][y] = func(x, y)
+			end
+			return results[x][y]
+		end
+	end
+end
+
 --[[
 Memoized variant of the Y combinator. Useful for caching results of recursive
 functions, so that previously computed inputs are not recomputed.