Fix #1638

src/Common/ArgumentBuilder.cs

@@ -0,0 +1,29 @@
+
+using System;
+using System.CommandLine;
+using System.Reflection;
+
+internal static class ArgumentBuilder
+{
+    private static readonly ConstructorInfo _ctor;
+
+    static ArgumentBuilder()
+    {
+        _ctor = typeof(Argument<string>).GetConstructor(new[] { typeof(string), typeof(string) });
+    }
+
+    public static Argument CreateArgument(Type valueType, string name = "value")
+    {
+        var argumentType = typeof(Argument<>).MakeGenericType(valueType);
+
+#if NET6_0_OR_GREATER
+            var ctor = (ConstructorInfo)argumentType.GetMemberWithSameMetadataDefinitionAs(_ctor);
+#else
+        var ctor = argumentType.GetConstructor(new[] { typeof(string), typeof(string) });
+#endif
+
+        var option = (Argument)ctor.Invoke(new object[] { name, null });
+
+        return option;
+    }
+}

src/Common/OptionBuilder.cs

@@ -0,0 +1,31 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Reflection;
+
+namespace System.CommandLine.Utility;
+
+internal static class OptionBuilder
+{
+    private static readonly ConstructorInfo _ctor;
+
+    static OptionBuilder()
+    {
+        _ctor = typeof(Option<string>).GetConstructor(new[] { typeof(string), typeof(string) });
+    }
+
+    public static Option CreateOption(string name, Type valueType)
+    {
+        var optionType = typeof(Option<>).MakeGenericType(valueType);
+
+#if NET6_0_OR_GREATER
+            var ctor = (ConstructorInfo)optionType.GetMemberWithSameMetadataDefinitionAs(_ctor);
+#else
+        var ctor = optionType.GetConstructor(new[] { typeof(string), typeof(string) });
+#endif
+
+        var option = (Option)ctor.Invoke(new object[] { name, null });
+
+        return option;
+    }
+}

src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt

@@ -1,12 +1,10 @@
 System.CommandLine
-  public class Argument : Symbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
-    .ctor()
-    .ctor(System.String name = null, System.String description = null)
+  public abstract class Argument : Symbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
     public ArgumentArity Arity { get; set; }
     public CompletionSourceList Completions { get; }
     public System.Boolean HasDefaultValue { get; }
     public System.String HelpName { get; set; }
-    public System.Type ValueType { get; set; }
+    public System.Type ValueType { get; }
     public System.Void AddValidator(System.CommandLine.Parsing.ValidateSymbolResult<System.CommandLine.Parsing.ArgumentResult> validate)
     public System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem> GetCompletions(System.CommandLine.Completions.CompletionContext context)
     public System.Object GetDefaultValue()
@@ -21,7 +19,7 @@
     .ctor(Func<T> getDefaultValue)
     .ctor(System.String name, ParseArgument<T> parse, System.Boolean isDefault = False, System.String description = null)
     .ctor(ParseArgument<T> parse, System.Boolean isDefault = False)
-    public System.Type ValueType { get; set; }
+    public System.Type ValueType { get; }
   public struct ArgumentArity : System.ValueType, System.IEquatable<ArgumentArity>
     public static ArgumentArity ExactlyOne { get; }
     public static ArgumentArity OneOrMore { get; }
@@ -181,9 +179,7 @@
     public System.String UnrecognizedCommandOrArgument(System.String arg)
     public System.String VersionOptionCannotBeCombinedWithOtherArguments(System.String optionAlias)
     public System.String VersionOptionDescription()
-  public class Option : IdentifierSymbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
-    .ctor(System.String name, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
-    .ctor(System.String[] aliases, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
+  public abstract class Option : IdentifierSymbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
     public System.Boolean AllowMultipleArgumentsPerToken { get; set; }
     public System.String ArgumentHelpName { get; set; }
     public ArgumentArity Arity { get; set; }

src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_Bare.cs

@@ -22,8 +22,9 @@ public class Perf_Parser_Options_Bare
         private IEnumerable<Option> GenerateTestOptions(int count, ArgumentArity arity)
             => Enumerable.Range(0, count)
                          .Select(i =>
-                                     new Option($"-option{i}", arity: arity)
+                                     new Option<string>($"-option{i}")
                                      {
+                                         Arity = arity,
                                          Description = $"Description for -option {i} ...."
                                      }
                          );
@@ -50,7 +51,7 @@ public void SetupTestOptions()
         [Benchmark]
         public Parser ParserFromOptions_Ctor()
         {
-            return Utils.CreateParser(_testSymbols);
+            return _testSymbols.CreateParser();
         }
 
         [GlobalSetup(Target = nameof(ParserFromOptions_Parse))]

src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_With_Arguments.cs

@@ -20,8 +20,9 @@ public class Perf_Parser_Options_With_Arguments
 
         private IEnumerable<Option> GenerateTestOptions(int count, ArgumentArity arity)
             => Enumerable.Range(0, count)
-                         .Select(i => new Option($"-option{i}", arity: arity)
+                         .Select(i => new Option<string>($"-option{i}")
                              {
+                                 Arity = arity,
                                  Description = $"Description for -option {i} ...."
                              }
                          );

src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_ParseResult.cs

@@ -20,7 +20,7 @@ public class Perf_Parser_ParseResult
 
         public Perf_Parser_ParseResult()
         {
-            var option = new Option("-opt");
+            var option = new Option<bool>("-opt");
 
             _testParser =
                 new CommandLineBuilder(new RootCommand { option })

src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_TypoCorrection.cs

@@ -22,7 +22,7 @@ public class Perf_Parser_TypoCorrection
 
         public Perf_Parser_TypoCorrection()
         {
-            var option = new Option("--0123456789");
+            var option = new Option<bool>("--0123456789");
 
             _testParser = new CommandLineBuilder(new RootCommand { option })
                           .UseTypoCorrections()

src/System.CommandLine.Benchmarks/CommandLine/Perf_Suggestions.cs

@@ -29,15 +29,15 @@ private string[] GenerateSuggestionsArray(int count)
 
         private IEnumerable<Option> GenerateOptionsArray(int count)
             => Enumerable.Range(0, count)
-                         .Select(i => new Option($"suggestion{i}"));
+                         .Select(i => new Option<string>($"suggestion{i}"));
 
         [Params(1, 5, 20, 100)]
         public int TestSuggestionsCount;
 
         [GlobalSetup(Target = nameof(SuggestionsFromSymbol))]
         public void Setup_FromSymbol()
         {
-            _testSymbol = new Option("--hello", arity: ArgumentArity.ExactlyOne)
+            _testSymbol = new Option<string>("--hello")
                 .AddCompletions(GenerateSuggestionsArray(TestSuggestionsCount));
         }
 

src/System.CommandLine.DragonFruit/CommandLine.cs

@@ -8,6 +8,7 @@
 using System.CommandLine.NamingConventionBinder;
 using System.CommandLine.Parsing;
 using System.CommandLine.Rendering;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -163,18 +164,13 @@ public static void ConfigureFromMethod(
                 command.AddOption(option);
             }
 
-            if (method.GetParameters()
-                      .FirstOrDefault(p => _argumentParameterNames.Contains(p.Name)) is ParameterInfo argsParam)
+            if (method.GetParameters().FirstOrDefault(p => _argumentParameterNames.Contains(p.Name)) is { } argsParam)
             {
-                var argument = new Argument
-                {
-                    ValueType = argsParam.ParameterType,
-                    Name = argsParam.Name
-                };
+                var argument = ArgumentBuilder.CreateArgument(argsParam.ParameterType, argsParam.Name);
 
                 if (argsParam.HasDefaultValue)
                 {
-                    if (argsParam.DefaultValue != null)
+                    if (argsParam.DefaultValue is not null)
                     {
                         argument.SetDefaultValue(argsParam.DefaultValue);
                     }
@@ -296,11 +292,17 @@ public static Option BuildOption(this ParameterDescriptor parameter)
             {
                 getDefaultValue = parameter.GetDefaultValue;
             }
-            return new Option(
-                parameter.BuildAlias(),
-                parameter.ValueName,
-                parameter.ValueType,
-                getDefaultValue);
+
+            var option = OptionBuilder.CreateOption(parameter.BuildAlias(), parameter.ValueType);
+
+            option.Description = parameter.ValueName;
+
+            if (getDefaultValue is not null)
+            {
+                option.SetDefaultValueFactory(getDefaultValue);
+            }
+
+            return option;
         }
 
         private static string GetDefaultXmlDocsFileLocation(Assembly assembly)

src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj

@@ -12,4 +12,9 @@
     <ProjectReference Include="..\System.CommandLine.NamingConventionBinder\System.CommandLine.NamingConventionBinder.csproj" />
     <Content Include="targets/*" PackagePath="build/$(TargetFramework)/" />
   </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\Common\ArgumentBuilder.cs" Link="Utility\ArgumentBuilder.cs" />
+    <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
+  </ItemGroup>
 </Project>

src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs

@@ -6,6 +6,7 @@
 using System.CommandLine.Invocation;
 using System.CommandLine.Parsing;
 using System.CommandLine.Tests.Binding;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -30,7 +31,7 @@ public void Option_arguments_are_bound_by_name_to_constructor_parameters(
 
         var command = new Command("the-command")
         {
-            new Option("--value", argumentType: type)
+            OptionBuilder.CreateOption("--value", type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -57,11 +58,7 @@ public void Command_arguments_are_bound_by_name_to_constructor_parameters(
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -84,11 +81,7 @@ public void Command_arguments_are_bound_by_name_to_complex_constructor_parameter
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -135,7 +128,7 @@ public void Option_arguments_are_bound_by_name_to_property_setters(
 
         var command = new Command("the-command")
         {
-            new Option("--value", argumentType: type)
+            OptionBuilder.CreateOption("--value", type)
         };
         var parser = new Parser(command);
 
@@ -163,11 +156,7 @@ public void Command_arguments_are_bound_by_name_to_property_setters(
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
         var parser = new Parser(command);
 

src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs

@@ -1,10 +1,10 @@
 // // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-using System.CommandLine.Binding;
 using System.CommandLine.Invocation;
 using System.CommandLine.IO;
 using System.CommandLine.Tests.Binding;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -35,7 +35,7 @@ public async Task Option_arguments_are_bound_by_name_to_method_parameters(
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
@@ -67,7 +67,7 @@ public async Task Option_arguments_are_bound_by_name_to_the_properties_of_method
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
@@ -99,7 +99,7 @@ public async Task Option_arguments_are_bound_by_name_to_the_constructor_paramete
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
@@ -127,11 +127,7 @@ public async Task Command_arguments_are_bound_by_name_to_handler_method_paramete
 
             var command = new Command("the-command")
             {
-                new Argument
-                {
-                    Name = "value",
-                    ValueType = type
-                }
+                ArgumentBuilder.CreateArgument(type)
             };
 
             var console = new TestConsole();