Reduce boilerplate needed for IValueParser implementations

src/CommandLineUtils/Abstractions/ValueParserProvider.cs

@@ -21,18 +21,18 @@ internal ValueParserProvider()
             AddRange(
                 new IValueParser[]
                 {
-                    StringValueParser.Singleton,
-                    BooleanValueParser.Singleton,
-                    ByteValueParser.Singleton,
-                    Int16ValueParser.Singleton,
-                    Int32ValueParser.Singleton,
-                    Int64ValueParser.Singleton,
-                    UInt16ValueParser.Singleton,
-                    UInt32ValueParser.Singleton,
-                    UInt64ValueParser.Singleton,
-                    FloatValueParser.Singleton,
-                    DoubleValueParser.Singleton,
-                    UriValueParser.Singleton,
+                    StockValueParsers.String,
+                    StockValueParsers.Boolean,
+                    StockValueParsers.Byte,
+                    StockValueParsers.Int16,
+                    StockValueParsers.Int32,
+                    StockValueParsers.Int64,
+                    StockValueParsers.UInt16,
+                    StockValueParsers.UInt32,
+                    StockValueParsers.UInt64,
+                    StockValueParsers.Float,
+                    StockValueParsers.Double,
+                    StockValueParsers.Uri,
                 });
         }
 
@@ -96,14 +96,14 @@ internal IValueParser GetParserImpl<T>()
 
             if (typeInfo.IsEnum)
             {
-                return new EnumParser(type);
+                return EnumParser.Create(type);
             }
 
             if (ReflectionHelper.IsNullableType(typeInfo, out var wrappedType))
             {
                 if (wrappedType.GetTypeInfo().IsEnum)
                 {
-                    return new NullableValueParser(new EnumParser(wrappedType));
+                    return new NullableValueParser(EnumParser.Create(wrappedType));
                 }
 
                 if (_parsers.TryGetValue(wrappedType, out parser))
@@ -125,8 +125,8 @@ internal IValueParser GetParserImpl<T>()
                 {
                     return null;
                 }
-                var parserType = typeof(ValueTupleValueParser<>).MakeGenericType(typeInfo.GenericTypeArguments[1]);
-                return (IValueParser)Activator.CreateInstance(parserType, new object[] { innerParser });
+                var method = typeof(ValueTupleValueParser).GetTypeInfo().GetMethod(nameof(ValueTupleValueParser.Create)).MakeGenericMethod(typeInfo.GenericTypeArguments[1]);
+                return (IValueParser)method.Invoke(null, new object[] { innerParser });
             }
 
             return null;

src/CommandLineUtils/Internal/ValueParsers/EnumParser.cs

@@ -6,27 +6,22 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Abstractions
 {
-    internal class EnumParser : IValueParser
+    internal static class EnumParser
     {
-        public EnumParser(Type enumType)
-        {
-            TargetType = enumType;
-        }
-
-        public Type TargetType { get; }
-
-        public object Parse(string argName, string value, CultureInfo culture)
-        {
-            if (value == null) return Enum.ToObject(TargetType, 0);
-
-            try
+        public static IValueParser Create(Type enumType) =>
+            ValueParser.Create(enumType, (argName, value, culture) =>
             {
-                return Enum.Parse(TargetType, value, ignoreCase: true);
-            }
-            catch
-            {
-                throw new FormatException($"Invalid value specified for {argName}. Allowed values are: {string.Join(", ", Enum.GetNames(TargetType))}.");
-            }
-        }
+                if (value == null) return Enum.ToObject(enumType, 0);
+
+                try
+                {
+                    return Enum.Parse(enumType, value, ignoreCase: true);
+                }
+                catch
+                {
+                    throw new FormatException(
+                        $"Invalid value specified for {argName}. Allowed values are: {string.Join(", ", Enum.GetNames(enumType))}.");
+                }
+            });
     }
 }