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petertsengpetertseng
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react: complete exercise
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‎exercises/react/example/Reactor.ceylon

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,5 @@
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import ceylon.collection { HashMap, MutableMap }
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alias Element => Integer;
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class Reactor() {
@@ -20,6 +22,7 @@ class Reactor() {
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assign currentValue {
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currentValue_ = currentValue;
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eachDependent((d) => d.propagate());
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eachDependent((d) => d.fireCallbacks());
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}
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}
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@@ -28,16 +31,46 @@ class Reactor() {
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}
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shared class ComputeCell(Element() newValue) extends Cell() {
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shared alias Callback => Anything(Element);
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variable Element currentValue_ = newValue();
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variable Element lastCallbackValue = currentValue_;
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shared actual Element currentValue => currentValue_;
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variable Integer callbacksIssued = 0;
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variable MutableMap<Integer, Callback> activeCallbacks = HashMap<Integer, Callback>();
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shared interface Subscription {
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shared formal void cancel();
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}
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shared Subscription addCallback(Callback f) {
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value id = callbacksIssued;
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callbacksIssued++;
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activeCallbacks.put(id, f);
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return object satisfies Subscription {
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cancel() => activeCallbacks.remove(id);
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};
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}
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shared void propagate() {
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value nv = newValue();
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if (nv != currentValue) {
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currentValue_ = nv;
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eachDependent((d) => d.propagate());
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}
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}
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shared void fireCallbacks() {
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if (lastCallbackValue == currentValue) {
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return;
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}
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lastCallbackValue = currentValue;
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for (cb in activeCallbacks.items) {
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cb(currentValue);
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}
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eachDependent((d) => d.fireCallbacks());
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}
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}
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shared ComputeCell newComputeCell1(Cell c, Element(Element) f) {

‎exercises/react/example/module.ceylon

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@@ -0,0 +1,4 @@
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module react "1.0" {
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import "ceylon.collection" "1.3.1";
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import "ceylon.test" "1.3.1";
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}

‎exercises/react/source/react/Reactor.ceylon

Lines changed: 37 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1 +1,37 @@
1-
// TODO
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alias Element => Integer;
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class Reactor() {
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shared abstract class Cell() {
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shared formal Element currentValue;
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}
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shared class InputCell(Element initialValue) extends Cell() {
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shared actual variable Element currentValue = nothing;
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}
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shared InputCell newInputCell(Element initialValue) {
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return nothing;
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}
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shared class ComputeCell(Element() newValue) extends Cell() {
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shared alias Callback => Anything(Element);
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shared actual Element currentValue = nothing;
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shared interface Subscription {
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shared formal void cancel();
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}
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shared Subscription addCallback(Callback f) {
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return nothing;
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}
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}
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shared ComputeCell newComputeCell1(Cell c, Element(Element) f) {
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return nothing;
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}
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shared ComputeCell newComputeCell2(Cell c1, Cell c2, Element(Element, Element) f) {
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return nothing;
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}
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}

‎exercises/react/source/react/ReactorTest.ceylon

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Original file line numberDiff line numberDiff line change
@@ -40,3 +40,122 @@ void computeCellsUpdateValueWhenDependenciesChange() {
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input.currentValue = 3;
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assertEquals(output.currentValue, 4);
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}
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test
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void computeCellsCanDependOnOtherComputeCells() {
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value r = Reactor();
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value input = r.newInputCell(1);
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value timesTwo = r.newComputeCell1(input, (x) => x * 2);
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value timesThirty = r.newComputeCell1(input, (x) => x * 30);
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value output = r.newComputeCell2(timesTwo, timesThirty, (x, y) => x + y);
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assertEquals(output.currentValue, 32);
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input.currentValue = 3;
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assertEquals(output.currentValue, 96);
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}
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test
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void computeCellsFireCallbacks() {
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value r = Reactor();
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value input = r.newInputCell(1);
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value output = r.newComputeCell1(input, (x) => x + 1);
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variable Element[] vals = [];
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output.addCallback((x) => vals = vals.withTrailing(x));
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input.currentValue = 3;
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assertEquals(vals, [4]);
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}
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test
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void callbacksOnlyFireOnChange() {
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value r = Reactor();
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value input = r.newInputCell(1);
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value output = r.newComputeCell1(input, (x) => if (x < 3) then 111 else 222);
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variable Element[] vals = [];
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output.addCallback((x) => vals = vals.withTrailing(x));
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input.currentValue = 2;
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assertEquals(vals, []);
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input.currentValue = 4;
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assertEquals(vals, [222]);
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}
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test
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void callbacksCanBeAddedAndRemoved() {
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value r = Reactor();
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value input = r.newInputCell(11);
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value output = r.newComputeCell1(input, (x) => x + 1);
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variable Element[] vals1 = [];
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value sub1 = output.addCallback((x) => vals1 = vals1.withTrailing(x));
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variable Element[] vals2 = [];
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output.addCallback((x) => vals2 = vals2.withTrailing(x));
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input.currentValue = 31;
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sub1.cancel();
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variable Element[] vals3 = [];
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output.addCallback((x) => vals3 = vals3.withTrailing(x));
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input.currentValue = 41;
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assertEquals(vals1, [32]);
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assertEquals(vals2, [32, 42]);
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assertEquals(vals3, [42]);
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}
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test
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void removingCallbackMultipleTimesDoesntInterfereWithOtherCallbacks() {
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value r = Reactor();
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value input = r.newInputCell(1);
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value output = r.newComputeCell1(input, (x) => x + 1);
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variable Element[] vals1 = [];
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value sub1 = output.addCallback((x) => vals1 = vals1.withTrailing(x));
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variable Element[] vals2 = [];
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output.addCallback((x) => vals2 = vals2.withTrailing(x));
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for (i in 1..10) {
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sub1.cancel();
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}
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input.currentValue = 2;
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assertEquals(vals1, []);
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assertEquals(vals2, [3]);
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}
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test
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void callbacksAreOnlyCalledOnceEvenIfMultipleDependenciesChange() {
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value r = Reactor();
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value input = r.newInputCell(1);
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value plusOne = r.newComputeCell1(input, (x) => x + 1);
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value minusOne1 = r.newComputeCell1(input, (x) => x - 1);
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value minusOne2 = r.newComputeCell1(minusOne1, (x) => x - 1);
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value output = r.newComputeCell2(plusOne, minusOne2, (x, y) => x * y);
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variable Element[] vals = [];
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output.addCallback((x) => vals = vals.withTrailing(x));
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input.currentValue = 4;
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assertEquals(vals, [10]);
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}
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test
147+
void callbacksAreNotCalledIfDependenciesChangeButOutputValueDoesntChange() {
148+
value r = Reactor();
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value input = r.newInputCell(1);
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value plusOne = r.newComputeCell1(input, (x) => x + 1);
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value minusOne = r.newComputeCell1(input, (x) => x - 1);
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value alwaysTwo = r.newComputeCell2(plusOne, minusOne, (x, y) => x - y);
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variable Element[] vals = [];
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alwaysTwo.addCallback((x) => vals = vals.withTrailing(x));
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for (i in 1..10) {
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input.currentValue = i;
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}
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assertEquals(vals, []);
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}

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