perf: call mapper as-is in mapped()

benches/mapped.luau

@@ -3,55 +3,56 @@ local bench = require("./bench")
 
 local computed = Charm.computed
 local mapped = Charm.mapped
-local setActiveSub = Charm.setActiveSub
 local signal = Charm.signal
 
-type Entry = { number }
+type Key = number
+type Value = number
 
 local count = 512
-local initialState: { Entry } = table.create(count)
+local initialState: { [Key]: Value } = table.create(count, 0)
 
-for i = 1, count do
-	initialState[i] = table.create(64, i)
+local function expensiveOperation()
+	for _ = 1, 100 do
+		continue
+	end
 end
 
-local function mapper(value: Entry, key: number): (Entry, number)
-	return table.clone(value), key + 1
-end
-
-local function simpleMapped(source: () -> { Entry }, mapper: (Entry, number) -> (Entry, number)): () -> { Entry }
+local function simpleMapped(
+	source: () -> { [Key]: Value },
+	mapper: (Value, Key) -> (Value, Key?)
+): () -> { [Key]: Value }
 	return computed(function()
 		local state = source()
 		local nextState = {}
 
-		for index, value in state do
-			local currentSub = setActiveSub(nil)
-			local success, valueOut, keyOut = pcall(mapper, value, index)
-			setActiveSub(currentSub)
-
-			if success then
-				nextState[keyOut] = valueOut
-			end
+		for keyIn, valueIn in state do
+			local valueOut, keyOut = mapper(valueIn, keyIn)
+			nextState[if keyOut == nil then keyIn else keyOut] = valueOut
 		end
 
-		return state
+		return nextState
 	end)
 end
 
-local function updatePercentage(percent: number): ({ Entry }) -> { Entry }
+local function updateRandomly(updateChance: number): ({ [Key]: Value }) -> { [Key]: Value }
 	return function(state)
 		local nextState = table.clone(state)
-		for index, value in state do
-			if math.random() < percent then
-				nextState[index] = table.clone(value)
+		for key in state do
+			if math.random() < updateChance then
+				nextState[key] += 1
 			end
 		end
 		return nextState
 	end
 end
 
-for _, percent in { 0.1, 0.5, 1 } do
-	bench.run(`mapped {percent}`, function()
+for _, updateChance in { 0.1, 0.5, 1 } do
+	local function mapper(value: Value, key: Key): (Value, Key?)
+		expensiveOperation()
+		return value + 1, key + 1
+	end
+
+	bench.run(`mapped {updateChance}`, function()
 		local src, setSrc = signal(initialState)
 		local out = mapped(src, mapper)
 
@@ -59,14 +60,14 @@ for _, percent in { 0.1, 0.5, 1 } do
 		out()
 		bench.profileend()
 
-		setSrc(updatePercentage(percent))
+		setSrc(updateRandomly(updateChance))
 
 		bench.profilebegin("update")
 		out()
 		bench.profileend()
 	end)
 
-	bench.run(`control {percent}`, function()
+	bench.run(`control {updateChance}`, function()
 		local src, setSrc = signal(initialState)
 		local out = simpleMapped(src, mapper)
 
@@ -74,7 +75,7 @@ for _, percent in { 0.1, 0.5, 1 } do
 		out()
 		bench.profileend()
 
-		setSrc(updatePercentage(percent))
+		setSrc(updateRandomly(updateChance))
 
 		bench.profilebegin("update")
 		out()

packages/charm/src/init.luau

@@ -914,22 +914,9 @@ end
 	@see https://github.com/littensy/charm?tab=readme-ov-file#mappedgetter-mapper
 ]]
 local function mapped<KI, VI, KO, VO>(getter: Getter<{ [KI]: VI }>, mapper: (VI, KI) -> (VO, KO)): Getter<{ [KO]: VO }>
-	local map = noYield(mapper)
 	local nextInput: { [KI]: VI } = {}
 	local keyMap: { [KI]: KO } = {}
 
-	local function mapUntracked(value: VI, key: KI): (VO, KO)
-		local prevSub = setActiveSub(nil)
-		local success, valueOut, keyOut = pcall(map, value, key)
-		activeSub = prevSub
-
-		if not success then
-			error(`mapped() transform function failed: {valueOut}`, 0)
-		end
-
-		return valueOut, if keyOut == nil then key :: any else keyOut
-	end
-
 	return computed(function(lastOutput: { [KO]: VO }?): { [KO]: VO }
 		local nextOutput: { [KO]: VO } = lastOutput or {}
 		local prevInput = nextInput
@@ -937,19 +924,19 @@ local function mapped<KI, VI, KO, VO>(getter: Getter<{ [KI]: VI }>, mapper: (VI,
 
 		-- For keys that were removed from the input, remove the corresponding
 		-- keys from the output.
-		for prevKeyIn in prevInput do
-			if nextInput[prevKeyIn] ~= nil then
+		for keyIn in prevInput do
+			if nextInput[keyIn] ~= nil then
 				continue
 			end
 
-			local prevKeyOut = keyMap[prevKeyIn]
+			local keyOut = keyMap[keyIn]
 
-			if prevKeyOut ~= nil then
+			if keyOut ~= nil then
 				if nextOutput == lastOutput then
 					nextOutput = table.clone(nextOutput)
 				end
-				nextOutput[prevKeyOut] = nil
-				keyMap[prevKeyIn] = nil
+				nextOutput[keyOut] = nil
+				keyMap[keyIn] = nil
 			end
 		end
 
@@ -957,13 +944,14 @@ local function mapped<KI, VI, KO, VO>(getter: Getter<{ [KI]: VI }>, mapper: (VI,
 		-- the output. If the mapper returns a new key that is different from
 		-- the previous call, the old mapped key should be removed from the
 		-- output.
-		for nextKeyIn, nextValueIn in nextInput do
-			if nextValueIn == prevInput[nextKeyIn] then
+		for keyIn, nextValueIn in nextInput do
+			if nextValueIn == prevInput[keyIn] then
 				continue
 			end
 
-			local nextValueOut, nextKeyOut = mapUntracked(nextValueIn, nextKeyIn)
-			local prevKeyOut = keyMap[nextKeyIn]
+			local nextValueOut, keyOutOrNil = mapper(nextValueIn, keyIn)
+			local nextKeyOut: KO = if keyOutOrNil ~= nil then keyOutOrNil else keyIn :: any
+			local prevKeyOut = keyMap[keyIn]
 
 			if prevKeyOut ~= nil and prevKeyOut ~= nextKeyOut then
 				if nextOutput == lastOutput then
@@ -971,13 +959,13 @@ local function mapped<KI, VI, KO, VO>(getter: Getter<{ [KI]: VI }>, mapper: (VI,
 				end
 				nextOutput[prevKeyOut] = nil
 				nextOutput[nextKeyOut] = nextValueOut
-				keyMap[nextKeyIn] = nextKeyOut
+				keyMap[keyIn] = nextKeyOut
 			elseif nextOutput[nextKeyOut] ~= nextValueOut then
 				if nextOutput == lastOutput then
 					nextOutput = table.clone(nextOutput)
 				end
 				nextOutput[nextKeyOut] = nextValueOut
-				keyMap[nextKeyIn] = nextKeyOut
+				keyMap[keyIn] = nextKeyOut
 			end
 		end