Added AutoEvent

.gitignore

@@ -10,4 +10,5 @@ obj/
 .DS_Store
 *.DotSettings.user
 *.binlog
+*.g.cs
 Chickensoft.Sync.Benchmarks/BenchmarkDotNet.Artifacts/

Chickensoft.Sync.Tests/src/primitives/AutoEventTest.cs

@@ -0,0 +1,207 @@
+namespace Chickensoft.Sync.Tests.Primitives;
+
+using System;
+using Shouldly;
+using Sync.Primitives;
+
+public sealed class AutoEventTest
+{
+  private sealed class TestEventArgs(string message)
+  {
+    public string Message { get; } = message;
+  }
+
+  private sealed class EventSource
+  {
+    public event Action? TestEventZero;
+    public event Action<TestEventArgs>? TestEventOne;
+    public event Action<object, TestEventArgs>? TestEventTwo;
+    public void FireZero() => TestEventZero?.Invoke();
+    public void FireOne(string message) => TestEventOne?.Invoke(new TestEventArgs(message));
+    public void FireTwo(string message) => TestEventTwo?.Invoke(this, new TestEventArgs(message));
+  }
+
+  private static AutoEvent<TestEventArgs> Wrap(EventSource source) =>
+    new(h => source.TestEventOne += h, h => source.TestEventOne -= h);
+
+  [Fact]
+  public void Initializes()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var raised = false;
+
+    autoEvent.Bind().On(_ => raised = true);
+
+    raised.ShouldBeFalse();
+  }
+
+  [Fact]
+  public void ForwardsEventToBindingsWithParamsZero()
+  {
+    var source = new EventSource();
+    var autoEvent = new AutoEvent(
+      action => source.TestEventZero += action,
+      action => source.TestEventZero -= action
+    );
+    bool? received = null;
+
+    autoEvent.Bind().On(() => received = true);
+
+    source.FireZero();
+
+    received.ShouldBe(true);
+  }
+
+  [Fact]
+  public void ForwardsEventToBindingsWithParamsOne()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    string? received = null;
+
+    autoEvent.Bind().On(args => received = args.Message);
+
+    source.FireOne("hello");
+
+    received.ShouldBe("hello");
+  }
+
+  [Fact]
+  public void ForwardsEventToBindingsWithParamsTwo()
+  {
+    var source = new EventSource();
+    var autoEvent = new AutoEvent<object, TestEventArgs>(
+      action => source.TestEventTwo += action,
+      action => source.TestEventTwo -= action
+    );
+    string? received = null;
+    object? obj = null;
+
+    autoEvent.Bind().On((sender, args) =>
+    {
+      received = args.Message;
+      obj = sender;
+    });
+
+    source.FireTwo("hello");
+
+    obj.ShouldBe(source);
+    received.ShouldBe("hello");
+  }
+
+  [Fact]
+  public void NoReentrancy()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var inCallback = false;
+    var reentered = false;
+
+    autoEvent.Bind().On(args =>
+    {
+      if (inCallback) { reentered = true; }
+      inCallback = true;
+      if (args.Message == "first") { source.FireOne("second"); }
+      inCallback = false;
+    });
+
+    source.FireOne("first");
+
+    reentered.ShouldBeFalse();
+  }
+
+  [Fact]
+  public void ConditionalCallbacks()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var all = new List<string>();
+    var helloOnly = new List<string>();
+
+    autoEvent.Bind()
+      .On(args => all.Add(args.Message))
+      .On(args => helloOnly.Add(args.Message), condition: args => args.Message == "hello");
+
+    source.FireOne("hello");
+    source.FireOne("world");
+    source.FireOne("hello");
+
+    all.ShouldBe(["hello", "world", "hello"]);
+    helloOnly.ShouldBe(["hello", "hello"]);
+  }
+
+  [Fact]
+  public void MultipleBindings()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var messages1 = new List<string>();
+    var messages2 = new List<string>();
+
+    autoEvent.Bind().On(args => messages1.Add(args.Message));
+    autoEvent.Bind().On(args => messages2.Add(args.Message));
+
+    source.FireOne("ping");
+
+    messages1.ShouldBe(["ping"]);
+    messages2.ShouldBe(["ping"]);
+  }
+
+  [Fact]
+  public void DisposedBindingStopsReceiving()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var messages = new List<string>();
+
+    var binding = autoEvent.Bind();
+    binding.On(args => messages.Add(args.Message));
+
+    source.FireOne("first");
+    messages.ShouldBe(["first"]);
+
+    binding.Dispose();
+
+    source.FireOne("second");
+    messages.ShouldBe(["first"]);
+  }
+
+  [Fact]
+  public void ClearsBindings()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var messages = new List<string>();
+
+    using var binding = autoEvent.Bind();
+    binding.On(args => messages.Add(args.Message));
+
+    source.FireOne("a");
+    source.FireOne("b");
+    messages.ShouldBe(["a", "b"]);
+    messages.Clear();
+
+    autoEvent.ClearBindings();
+    source.FireOne("c");
+    messages.ShouldBeEmpty();
+  }
+
+  [Fact]
+  public void DisposeUnsubscribesFromSource()
+  {
+    var source = new EventSource();
+    var autoEvent = Wrap(source);
+    var messages = new List<string>();
+
+    autoEvent.Bind().On(args => messages.Add(args.Message));
+
+    source.FireOne("before");
+    messages.ShouldBe(["before"]);
+
+    autoEvent.Dispose();
+
+    source.FireOne("after");
+    messages.ShouldBe(["before"]);
+  }
+}

Chickensoft.Sync/Chickensoft.Sync.csproj

@@ -29,12 +29,21 @@
 
     <RepositoryType>git</RepositoryType>
     <RepositoryUrl>https://github.com/chickensoft-games/Sync.git</RepositoryUrl>
+    <TransformOnBuild>true</TransformOnBuild>
+    <AfterTransform>AddGeneratedT4FilesToCompile;$(AfterTransform)</AfterTransform>
   </PropertyGroup>
 
+  <Target Name="AddGeneratedT4FilesToCompile">
+    <ItemGroup>
+      <Compile Include="@(GeneratedTemplates)" />
+    </ItemGroup>
+  </Target>
+
   <ItemGroup>
     <None Include="../README.md" Pack="true" PackagePath="\" />
     <None Include="../LICENSE" Pack="true" PackagePath="\" />
     <None Include="./icon.png" Pack="true" PackagePath="" />
+    <T4Transform Include="**\*.tt" />
   </ItemGroup>
 
   <ItemGroup>
@@ -47,5 +56,6 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="T4.BuildTools" Version="3.0.0" PrivateAssets="all" />
   </ItemGroup>
 </Project>

Chickensoft.Sync/src/primitives/AutoEvent.tt

@@ -0,0 +1,130 @@
+<#@ template debug="false" hostspecific="false" language="C#" #>
+<#@ assembly name="System.Core" #>
+<#@ import namespace="System.Linq" #>
+<#@ output extension=".g.cs" #>
+<#
+  const int maxArity = 16;
+#>
+namespace Chickensoft.Sync.Primitives;
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using Sync;
+<# for (int arity = 0; arity <= maxArity; arity++) {
+  var tp        = Enumerable.Range(1, arity).Select(i => $"T{i}").ToArray();
+  var tpList    = string.Join(", ", tp);
+  var tpBrk     = arity > 0 ? $"<{tpList}>" : "";
+  var argFields = string.Join(", ", tp.Select((t, i) => $"{t} Arg{i + 1}"));
+  var argParams = string.Join(", ", tp.Select((t, i) => $"{t} arg{i + 1}"));
+  var argValues = string.Join(", ", Enumerable.Range(1, arity).Select(i => $"arg{i}"));
+  var bcastArgs = string.Join(", ", Enumerable.Range(1, arity).Select(i => $"b.Arg{i}"));
+  var opArgs    = string.Join(", ", Enumerable.Range(1, arity).Select(i => $"op.Arg{i}"));
+  var actionType  = arity > 0 ? $"Action<{tpList}>" : "Action";
+  var funcType    = arity > 0 ? $"Func<{tpList}, bool>" : "Func<bool>";
+  var subType     = $"Action<{actionType}>";
+  var iCref       = arity > 0 ? $"IAutoEvent{{{tpList}}}" : "IAutoEvent";
+  var classCref   = arity > 0 ? $"AutoEvent{{{tpList}}}" : "AutoEvent";
+#>
+
+/// <summary>
+/// <para>
+/// An observable adapter for a C# event that forwards event firings to
+/// subscribers through the sync pipeline.
+/// </para>
+/// </summary>
+<# for (int i = 1; i <= arity; i++) { #>
+/// <typeparam name="T<#= i #>">Type of argument <#= i #>.</typeparam>
+<# } #>
+public interface IAutoEvent<#= tpBrk #> :
+  IAutoObject<AutoEvent<#= tpBrk #>.Binding>;
+
+/// <inheritdoc cref="<#= iCref #>"/>
+public sealed class AutoEvent<#= tpBrk #> :
+  IAutoEvent<#= tpBrk #>,
+  IPerform<AutoEvent<#= tpBrk #>.RaiseOp>
+{
+  // Atomic operations
+  private readonly record struct RaiseOp(<#= argFields #>);
+
+  // Broadcasts
+  private readonly record struct RaiseBroadcast(<#= argFields #>);
+
+  /// <summary>
+  /// A binding to an <see cref="<#= classCref #>"/>.
+  /// </summary>
+  public class Binding : SyncBinding
+  {
+    internal Binding(ISyncSubject subject) : base(subject) { }
+
+    /// <summary>
+    /// Registers a callback that is invoked whenever the event is raised.
+    /// </summary>
+    /// <param name="callback">Callback to invoke.</param>
+    /// <param name="condition">Optional condition that must be true for the
+    /// callback to be invoked.</param>
+    /// <returns>This binding (for chaining).</returns>
+    [
+      SuppressMessage(
+        "Style",
+        "IDE0350",
+        Justification = "Implicit lambda with ref type won't compile"
+      )
+    ]
+    public Binding On(
+      <#= actionType #> callback, <#= funcType #>? condition = null
+    )
+    {
+      bool predicate(<#= argParams #>) => condition?.Invoke(<#= argValues #>) ?? true;
+
+      AddCallback(
+        (in RaiseBroadcast b) => callback(<#= bcastArgs #>),
+        (in RaiseBroadcast b) => predicate(<#= bcastArgs #>)
+      );
+
+      return this;
+    }
+  }
+
+  private readonly SyncSubject _subject;
+  private readonly <#= subType #> _unsubscribe;
+
+  /// <summary>
+  /// <para>
+  /// Creates a new auto event that subscribes to a C# event and forwards
+  /// firings to its bindings through the sync pipeline.
+  /// </para>
+  /// </summary>
+  /// <param name="subscribe">Action that subscribes the internal handler to
+  /// the source event (e.g., <c>h => myObj.MyEvent += h</c>).</param>
+  /// <param name="unsubscribe">Action that unsubscribes the internal handler
+  /// from the source event (e.g., <c>h => myObj.MyEvent -= h</c>).</param>
+  public AutoEvent(
+    <#= subType #> subscribe,
+    <#= subType #> unsubscribe
+  )
+  {
+    _subject = new SyncSubject(this);
+    _unsubscribe = unsubscribe;
+    subscribe(OnEventRaised);
+  }
+
+  private void OnEventRaised(<#= argParams #>) =>
+    _subject.Perform(new RaiseOp(<#= argValues #>));
+
+  /// <inheritdoc />
+  public Binding Bind() => new(_subject);
+
+  /// <inheritdoc />
+  public void ClearBindings() => _subject.ClearBindings();
+
+  /// <inheritdoc />
+  public void Dispose()
+  {
+    _unsubscribe(OnEventRaised);
+    _subject.Dispose();
+  }
+
+  void IPerform<RaiseOp>.Perform(in RaiseOp op) =>
+    _subject.Broadcast(new RaiseBroadcast(<#= opArgs #>));
+}
+<# } #>

cspell.json

@@ -3,6 +3,7 @@
     "**/*.*"
   ],
   "ignorePaths": [
+    "**/*.tt",
     "**/*.tscn",
     "**/*.import",
     "**/badges/**/*.*",