Downgraded the library to netstandard2.0 for increased compatibility.

Author: leeoades

src/FunctionalStateMachine.CommandRunner/FunctionalStateMachine.CommandRunner.csproj

@@ -1,17 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net9.0</TargetFramework>
+        <TargetFramework>netstandard2.0</TargetFramework>
+        <LangVersion>latest</LangVersion>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
 
         <!-- Package metadata -->
         <Description>Command execution framework for FunctionalStateMachine with dependency injection support and source generation</Description>
     </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.12" />
-  </ItemGroup>
+    <!-- Polyfills for C# 9+ features on netstandard2.0 -->
+    <ItemGroup>
+        <PackageReference Include="PolySharp" Version="1.14.1" PrivateAssets="all" />
+        <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="2.0.0" />
+    </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\FunctionalStateMachine.CommandRunner.Generator\FunctionalStateMachine.CommandRunner.Generator.csproj"

src/FunctionalStateMachine.CommandRunner/ServiceCollectionExtensions.cs

@@ -8,7 +8,7 @@ public static IServiceCollection AddCommandRunners<TCommand>(
         this IServiceCollection services,
         CommandRunnerOptions? options = null)
     {
-        ArgumentNullException.ThrowIfNull(services);
+        if (services == null) throw new ArgumentNullException(nameof(services));
 
         var resolvedOptions = options ?? new CommandRunnerOptions();
         if (!CommandRunnerRegistry.TryGet<TCommand>(out var registration))

src/FunctionalStateMachine.Core/FunctionalStateMachine.Core.csproj

@@ -1,12 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net9.0</TargetFramework>
+        <TargetFramework>netstandard2.0</TargetFramework>
+        <LangVersion>latest</LangVersion>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
 
         <!-- Package metadata -->
         <Description>Functional state machine library for .NET with command-based side effects, perfect for actor-model architectures and event sourcing</Description>
     </PropertyGroup>
 
+    <!-- Polyfills for C# 9+ features on netstandard2.0 -->
+    <ItemGroup>
+        <PackageReference Include="PolySharp" Version="1.14.1" PrivateAssets="all" />
+    </ItemGroup>
+
 </Project>

src/FunctionalStateMachine.Core/StateMachineAnalysis.cs

@@ -241,10 +241,14 @@ private static void AnalyzeAmbiguousTransitions(
         IReadOnlyDictionary<TState, StateMachine<TState, TTrigger, TData, TCommand>.StateDefinition> states,
         AnalysisResult result)
     {
-        foreach (var (state, definition) in states)
+        foreach (var kvp in states)
         {
-            foreach (var (triggerKey, transitions) in definition.Transitions)
+            var state = kvp.Key;
+            var definition = kvp.Value;
+            foreach (var transitionKvp in definition.Transitions)
             {
+                var triggerKey = transitionKvp.Key;
+                var transitions = transitionKvp.Value;
                 // Find unguarded transitions
                 var unguardedTransitions = transitions.Where(t => t.Guard == null).ToList();
 
@@ -273,10 +277,14 @@ private static void AnalyzeConditionalTransitionTargets(
         IReadOnlyDictionary<TState, StateMachine<TState, TTrigger, TData, TCommand>.StateDefinition> states,
         AnalysisResult result)
     {
-        foreach (var (state, definition) in states)
+        foreach (var kvp in states)
         {
-            foreach (var (triggerKey, transitions) in definition.Transitions)
+            var state = kvp.Key;
+            var definition = kvp.Value;
+            foreach (var transitionKvp in definition.Transitions)
             {
+                var triggerKey = transitionKvp.Key;
+                var transitions = transitionKvp.Value;
                 foreach (var transition in transitions)
                 {
                     var maxTransitionCount = GetMaxTransitionCountPerPath(transition.Steps);
@@ -362,8 +370,10 @@ private static void AnalyzeDeadEndStates(
         TState initialState,
         AnalysisResult result)
     {
-        foreach (var (state, definition) in states)
+        foreach (var kvp in states)
         {
+            var state = kvp.Key;
+            var definition = kvp.Value;
             // Skip initial state - it's okay for it to be a dead-end (terminal state)
             if (state.Equals(initialState))
                 continue;

test/FunctionalStateMachine.CommandRunnerTests/FunctionalStateMachine.CommandRunnerTests.csproj

@@ -9,6 +9,7 @@
 
     <ItemGroup>
         <PackageReference Include="coverlet.collector" Version="6.0.2"/>
+        <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.0" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
         <PackageReference Include="xunit" Version="2.9.2"/>
         <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2"/>