Use ValueTask

.github/workflows/CD.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Install .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.0.100
+        dotnet-version: 3.1.100
 
     - name: Pack
       run: dotnet pack CliFx --configuration Release

.github/workflows/CI.yml

@@ -13,7 +13,7 @@ jobs:
     - name: Install .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.0.100
+        dotnet-version: 3.1.100
 
     - name: Build & test
       run: dotnet test --configuration Release

CliFx.Benchmarks/Benchmark.cs

@@ -4,17 +4,17 @@ using CliFx.Benchmarks.Commands;
 
 namespace CliFx.Benchmarks
 {
-    [CoreJob]
+    [SimpleJob]
     [RankColumn]
     public class Benchmark
     {
         private static readonly string[] Arguments = {"--str", "hello world", "-i", "13", "-b"};
 
         [Benchmark(Description = "CliFx", Baseline = true)]
-        public Task<int> ExecuteWithCliFx() => new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments);
+        public async ValueTask<int> ExecuteWithCliFx() => await new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments);
 
         [Benchmark(Description = "System.CommandLine")]
-        public Task<int> ExecuteWithSystemCommandLine() => new SystemCommandLineCommand().ExecuteAsync(Arguments);
+        public async ValueTask<int> ExecuteWithSystemCommandLine() => await new SystemCommandLineCommand().ExecuteAsync(Arguments);
 
         [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
         public int ExecuteWithMcMaster() => McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute<McMasterCommand>(Arguments);

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -3,14 +3,14 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.11.5" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
     <PackageReference Include="clipr" Version="1.6.1" />
     <PackageReference Include="CommandLineParser" Version="2.6.0" />
-    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.3.4" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.4.4" />
     <PackageReference Include="PowerArgs" Version="3.6.0" />
     <PackageReference Include="System.CommandLine.Experimental" Version="0.3.0-alpha.19317.1" />
   </ItemGroup>

CliFx.Benchmarks/Commands/CliFxCommand.cs

@@ -16,6 +16,6 @@ namespace CliFx.Benchmarks.Commands
         [CommandOption("bool", 'b')]
         public bool BoolOption { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Demo/CliFx.Demo.csproj

@@ -3,12 +3,12 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="2.2.0" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="3.1.0" />
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.2" />
+    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -31,7 +31,7 @@ namespace CliFx.Demo.Commands
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             // To make the demo simpler, we will just generate random publish date and ISBN if they were not set
             if (Published == default)
@@ -48,7 +48,7 @@ namespace CliFx.Demo.Commands
             console.Output.WriteLine("Book added.");
             console.RenderBook(book);
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 

CliFx.Demo/Commands/BookCommand.cs

@@ -20,7 +20,7 @@ namespace CliFx.Demo.Commands
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var book = _libraryService.GetBook(Title);
 
@@ -29,7 +29,7 @@ namespace CliFx.Demo.Commands
 
             console.RenderBook(book);
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Commands/BookListCommand.cs

@@ -16,7 +16,7 @@ namespace CliFx.Demo.Commands
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var library = _libraryService.GetLibrary();
 
@@ -32,7 +32,7 @@ namespace CliFx.Demo.Commands
                 console.RenderBook(book);
             }
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -19,7 +19,7 @@ namespace CliFx.Demo.Commands
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var book = _libraryService.GetBook(Title);
 
@@ -30,7 +30,7 @@ namespace CliFx.Demo.Commands
 
             console.Output.WriteLine($"Book {Title} removed.");
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Program.cs

@@ -25,11 +25,11 @@ namespace CliFx.Demo
             return services.BuildServiceProvider();
         }
 
-        public static Task<int> Main(string[] args)
+        public static async Task<int> Main(string[] args)
         {
             var serviceProvider = ConfigureServices();
 
-            return new CliApplicationBuilder()
+            return await new CliApplicationBuilder()
                 .AddCommandsFromThisAssembly()
                 .UseCommandFactory(schema => (ICommand) serviceProvider.GetRequiredService(schema.Type))
                 .Build()

CliFx.Tests/CliFx.Tests.csproj

@@ -2,7 +2,7 @@
   <Import Project="../CliFx.props" />
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <CollectCoverage>true</CollectCoverage>

CliFx.Tests/TestCommands/CancellableCommand.cs

@@ -8,7 +8,7 @@ namespace CliFx.Tests.TestCommands
     [Command("cancel")]
     public class CancellableCommand : ICommand
     {
-        public async Task ExecuteAsync(IConsole console)
+        public async ValueTask ExecuteAsync(IConsole console)
         {
             await Task.Yield();
 

CliFx.Tests/TestCommands/CommandExceptionCommand.cs

@@ -14,6 +14,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("msg", 'm')]
         public string? Message { get; set; }
         
-        public Task ExecuteAsync(IConsole console) => throw new CommandException(Message, ExitCode);
+        public ValueTask ExecuteAsync(IConsole console) => throw new CommandException(Message, ExitCode);
     }
 }

CliFx.Tests/TestCommands/ConcatCommand.cs

@@ -14,10 +14,10 @@ namespace CliFx.Tests.TestCommands
         [CommandOption('s', Description = "String separator.")]
         public string Separator { get; set; } = ""; 
         
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             console.Output.WriteLine(string.Join(Separator, Inputs));
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Tests/TestCommands/DivideCommand.cs

@@ -16,10 +16,10 @@ namespace CliFx.Tests.TestCommands
         // This property should be ignored by resolver
         public bool NotAnOption { get; set; }
         
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             console.Output.WriteLine(Dividend / Divisor);
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Tests/TestCommands/DuplicateOptionNamesCommand.cs

@@ -13,6 +13,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("fruits")]
         public string? Oranges { get; set; }
         
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/DuplicateOptionShortNamesCommand.cs

@@ -13,6 +13,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption('f')]
         public string? Oranges { get; set; }
         
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/EnvironmentVariableCommand.cs

@@ -10,6 +10,6 @@ namespace CliFx.Tests.TestCommands
 		[CommandOption("opt", EnvironmentVariableName = "ENV_SINGLE_VALUE")]
 		public string? Option { get; set; }
 
-		public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+		public ValueTask ExecuteAsync(IConsole console) => default;
 	}
 }

CliFx.Tests/TestCommands/EnvironmentVariableWithMultipleValuesCommand.cs

@@ -11,6 +11,6 @@ namespace CliFx.Tests.TestCommands
 		[CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
 		public IEnumerable<string>? Option { get; set; }
 
-		public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+		public ValueTask ExecuteAsync(IConsole console) => default;
 	}
 }

CliFx.Tests/TestCommands/EnvironmentVariableWithoutCollectionPropertyCommand.cs

@@ -10,6 +10,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
         public string? Option { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/ExceptionCommand.cs

@@ -11,6 +11,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("msg", 'm')]
         public string? Message { get; set; }
         
-        public Task ExecuteAsync(IConsole console) => throw new Exception(Message);
+        public ValueTask ExecuteAsync(IConsole console) => throw new Exception(Message);
     }
 }

CliFx.Tests/TestCommands/HelloWorldDefaultCommand.cs

@@ -7,10 +7,10 @@ namespace CliFx.Tests.TestCommands
     [Command]
     public class HelloWorldDefaultCommand : ICommand
     {
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             console.Output.WriteLine("Hello world.");
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Tests/TestCommands/HelpDefaultCommand.cs

@@ -13,6 +13,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("option-b", 'b', Description = "OptionB description.")]
         public string? OptionB { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/HelpNamedCommand.cs

@@ -13,6 +13,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("option-d", 'd', Description = "OptionD description.")]
         public string? OptionD { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/HelpSubCommand.cs

@@ -10,6 +10,6 @@ namespace CliFx.Tests.TestCommands
         [CommandOption("option-e", 'e', Description = "OptionE description.")]
         public string? OptionE { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Tests/TestCommands/NonAnnotatedCommand.cs

@@ -5,6 +5,6 @@ namespace CliFx.Tests.TestCommands
 {
     public class NonAnnotatedCommand : ICommand
     {
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx/CliApplication.cs

@@ -43,7 +43,7 @@ namespace CliFx
             _helpTextRenderer = helpTextRenderer;
         }
 
-        private async Task<int?> HandleDebugDirectiveAsync(CommandInput commandInput)
+        private async ValueTask<int?> HandleDebugDirectiveAsync(CommandInput commandInput)
         {
             // Debug mode is enabled if it's allowed in the application and it was requested via corresponding directive
             var isDebugMode = _configuration.IsDebugModeAllowed && commandInput.IsDebugDirectiveSpecified();
@@ -162,7 +162,7 @@ namespace CliFx
             return isError ? -1 : 0;
         }
 
-        private async Task<int> HandleCommandExecutionAsync(CommandInput commandInput, CommandSchema targetCommandSchema)
+        private async ValueTask<int> HandleCommandExecutionAsync(CommandInput commandInput, CommandSchema targetCommandSchema)
         {
             // Create an instance of the command
             var command = _commandFactory.CreateCommand(targetCommandSchema);
@@ -178,7 +178,7 @@ namespace CliFx
         }
 
         /// <inheritdoc />
-        public async Task<int> RunAsync(IReadOnlyList<string> commandLineArguments)
+        public async ValueTask<int> RunAsync(IReadOnlyList<string> commandLineArguments)
         {
             try
             {

CliFx/CliFx.csproj

@@ -2,7 +2,7 @@
   <Import Project="../CliFx.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>net45;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net45</TargetFrameworks>
     <Authors>$(Company)</Authors>
     <Description>Declarative framework for CLI applications</Description>
     <PackageTags>command line executable interface framework parser arguments net core</PackageTags>
@@ -18,15 +18,18 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
   </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0-preview.2" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0-beta2-19554-01" PrivateAssets="all" />
-    <PackageReference Include="Nullable" Version="1.1.1" PrivateAssets="all" />
-
-  </ItemGroup>
-
   <ItemGroup>
     <None Include="../favicon.png" Pack="True" PackagePath="" />
   </ItemGroup>
 
-</Project>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="all" />
+    <PackageReference Include="Nullable" Version="1.1.1" PrivateAssets="all" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net45'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.3" />
+  </ItemGroup>
+
+</Project>

CliFx/ICliApplication.cs

@@ -11,6 +11,6 @@ namespace CliFx
         /// <summary>
         /// Runs application with specified command line arguments and returns an exit code.
         /// </summary>
-        Task<int> RunAsync(IReadOnlyList<string> commandLineArguments);
+        ValueTask<int> RunAsync(IReadOnlyList<string> commandLineArguments);
     }
 }

CliFx/ICommand.cs

@@ -12,6 +12,6 @@ namespace CliFx
         /// Executes command using specified implementation of <see cref="IConsole"/>.
         /// This method is called when the command is invoked by a user through command line interface.
         /// </summary>
-        Task ExecuteAsync(IConsole console);
+        ValueTask ExecuteAsync(IConsole console);
     }
 }

Readme.md

@@ -59,8 +59,8 @@ The following code will create and run default `CliApplication` that will resolv
 ```c#
 public static class Program
 {
-    public static Task<int> Main(string[] args) =>
+    public static async Task<int> Main(string[] args) =>
-        new CliApplicationBuilder()
+        await new CliApplicationBuilder()
             .AddCommandsFromThisAssembly()
             .Build()
             .RunAsync(args);
@@ -85,17 +85,17 @@ public class LogCommand : ICommand
     [CommandOption("base", 'b', Description = "Logarithm base.")]
     public double Base { get; set; } = 10;
 
-    public Task ExecuteAsync(IConsole console)
+    public ValueTask ExecuteAsync(IConsole console)
     {
         var result = Math.Log(Value, Base);
         console.Output.WriteLine(result);
 
-        return Task.CompletedTask;
+        return default;
     }
 }
 ```
 
-By implementing `ICommand` this class also provides `ExecuteAsync` method. This is the method that gets called when the user invokes the command. Its return type is `Task` in order to facilitate asynchronous execution, but if your command runs synchronously you can simply return `Task.CompletedTask`.
+By implementing `ICommand` this class also provides `ExecuteAsync` method. This is the method that gets called when the user invokes the command. Its return type is `ValueTask` in order to facilitate both synchronous and asynchronous execution. If your command always runs synchronously, simply return `default` at the end of the method.
 
 The `ExecuteAsync` method also takes an instance of `IConsole` as a parameter. You should use the `console` parameter in places where you would normally use `System.Console`, in order to make your command testable.
 
@@ -171,7 +171,7 @@ public class DivideCommand : ICommand
     [CommandOption("divisor", IsRequired = true)]
     public double Divisor { get; set; }
 
-    public Task ExecuteAsync(IConsole console)
+    public ValueTask ExecuteAsync(IConsole console)
     {
         if (Math.Abs(Divisor) < double.Epsilon)
         {
@@ -182,7 +182,7 @@ public class DivideCommand : ICommand
         var result = Dividend / Divisor;
         console.Output.WriteLine(result);
 
-        return Task.CompletedTask;
+        return default;
     }
 }
 ```
@@ -225,7 +225,7 @@ Cancelled or terminated app returns non-zero exit code.
 [Command("cancel")]
 public class CancellableCommand : ICommand
 {
-    public async Task ExecuteAsync(IConsole console)
+    public async ValueTask ExecuteAsync(IConsole console)
     {
         console.Output.WriteLine("Printed");
 
@@ -248,7 +248,7 @@ For example, here is how you would configure your application to use [`Microsoft
 ```c#
 public static class Program
 {
-    public static Task<int> Main(string[] args)
+    public static async Task<int> Main(string[] args)
     {
         var services = new ServiceCollection();
 
@@ -260,7 +260,7 @@ public static class Program
 
         var serviceProvider = services.BuildServiceProvider();
 
-        return new CliApplicationBuilder()
+        return await new CliApplicationBuilder()
             .AddCommandsFromThisAssembly()
             .UseCommandFactory(schema => (ICommand) serviceProvider.GetRequiredService(schema.Type))
             .Build()
@@ -285,7 +285,7 @@ public class UserAddCommand : ICommand
     [CommandOption("email", 'e')]
     public string Email { get; set; }
 
-    public Task ExecuteAsync(IConsole console)
+    public ValueTask ExecuteAsync(IConsole console)
     {
         var validationResult = new UserAddCommandValidator().Validate(this);
         if (!validationResult.IsValid)
@@ -358,13 +358,13 @@ public class ConcatCommand : ICommand
     [CommandOption("right")]
     public string Right { get; set; } = "world";
 
-    public Task ExecuteAsync(IConsole console)
+    public ValueTask ExecuteAsync(IConsole console)
     {
         console.Output.Write(Left);
         console.Output.Write(' ');
         console.Output.Write(Right);
 
-        return Task.CompletedTask;
+        return default;
     }
 }
 ```