cleanup: simplify implementation of TypeDescriptor support and make code formatting consistent

Author: natemcmaster

src/CommandLineUtils/Abstractions/DefaultValueParserFactory.cs

@@ -15,7 +15,7 @@ namespace McMaster.Extensions.CommandLineUtils.Abstractions
     public class ValueParserProvider
     {
         private readonly Dictionary<Type, IValueParser> _parsers = new Dictionary<Type, IValueParser>(10);
-        private readonly DefaultValueParserFactory _defaultValueParserFactory = new DefaultValueParserFactory();
+        private readonly TypeDescriptorValueParserFactory _defaultValueParserFactory = new TypeDescriptorValueParserFactory();
 
         internal ValueParserProvider()
         {
@@ -102,7 +102,9 @@ public IValueParser GetParser(Type type)
             }
 
             if (_defaultValueParserFactory.TryGetParser<T>(out parser))
+            {
                 return parser;
+            }
 
             if (ReflectionHelper.IsNullableType(type, out var wrappedType) && wrappedType != null)
             {

src/CommandLineUtils/Abstractions/ValueParserProvider.cs

@@ -3,11 +3,10 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    using System.Globalization;
-
     internal class ArrayParser : ICollectionParser
     {
         private readonly Type _elementType;

src/CommandLineUtils/Internal/ValueParsers/ArrayParser.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Globalization;
 
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {

src/CommandLineUtils/Internal/ValueParsers/EnumParser.cs

@@ -3,12 +3,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Reflection;
 
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    using System.Globalization;
-
     internal class HashSetParser : ICollectionParser
     {
         private readonly IValueParser _elementParser;

src/CommandLineUtils/Internal/ValueParsers/HashSetParser.cs

@@ -1,11 +1,11 @@
 // Copyright (c) Nate McMaster.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Globalization;
+
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    using System;
-    using System.Globalization;
-
     internal class NullableValueParser : IValueParser
     {
         private readonly IValueParser _wrapped;

src/CommandLineUtils/Internal/ValueParsers/NullableValueParser.cs

@@ -1,11 +1,11 @@
 // Copyright (c) Nate McMaster.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Globalization;
+
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    using System;
-    using System.Globalization;
-
     internal static class StockValueParsers
     {
         public static readonly IValueParser<bool> Boolean = ValueParser.Create(

src/CommandLineUtils/Internal/ValueParsers/StockValueParsers.cs

@@ -0,0 +1,59 @@
+// Copyright (c) Nate McMaster.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.ComponentModel;
+using System.Globalization;
+
+namespace McMaster.Extensions.CommandLineUtils.Abstractions
+{
+    /// <summary>
+    /// A factory creating generic implementations of <see cref="IValueParser{T}"/>. The implementations are based
+    /// on automatically located <see cref="TypeConverter"/> classes that are suitable for parsing.
+    /// </summary>
+    internal class TypeDescriptorValueParserFactory
+    {
+        public bool TryGetParser<T>(out IValueParser parser)
+        {
+            var targetType = typeof(T);
+            var converter = TypeDescriptor.GetConverter(targetType);
+            if (converter.CanConvertFrom(typeof(string)))
+            {
+                parser = new TypeConverterValueParser<T>(targetType, converter);
+                return true;
+            }
+
+            parser = null;
+            return false;
+        }
+
+        private sealed class TypeConverterValueParser<T> : IValueParser<T>
+        {
+            public TypeConverterValueParser(Type targetType, TypeConverter typeConverter)
+            {
+                TargetType = targetType ?? throw new ArgumentNullException(nameof(targetType));
+                TypeConverter = typeConverter ?? throw new ArgumentNullException(nameof(typeConverter));
+            }
+
+            public Type TargetType { get; }
+
+            private TypeConverter TypeConverter { get; }
+
+            public T Parse(string argName, string value, CultureInfo culture)
+            {
+                try
+                {
+                    culture ??= CultureInfo.InvariantCulture;
+                    return (T)TypeConverter.ConvertFromString(null, culture, value);
+                }
+                catch (ArgumentException e)
+                {
+                    throw new FormatException(e.Message, e);
+                }
+            }
+
+            object IValueParser.Parse(string argName, string value, CultureInfo culture)
+                => Parse(argName, value, culture);
+        }
+    }
+}

src/CommandLineUtils/Internal/ValueParsers/TypeDescriptorValueParserFactory.cs

@@ -1,11 +1,11 @@
 // Copyright (c) Nate McMaster.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Globalization;
+
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    using System;
-    using System.Globalization;
-
     /// <summary>
     /// Provides methods for creating <see cref="IValueParser{T}"/>
     /// boilerplate implementations.

src/CommandLineUtils/Internal/ValueParsers/ValueParser.cs

@@ -508,7 +508,7 @@ public void ParsesGuid(string arg)
         [InlineData("")]
         public void ParsesGuidNullable(string arg)
         {
-            var expected = String.IsNullOrWhiteSpace(arg)
+            var expected = string.IsNullOrWhiteSpace(arg)
                 ? (Guid?)null
                 : Guid.Parse("ff23ef12-500a-48df-9a5d-151c2adc2a0a");
             var parsed = CommandLineParser.ParseArgs<Program>("--guid-opt", arg);