Proposed changes for enhancement:

#189

Author: jtongsbux

paket.lock

@@ -169,8 +169,16 @@
         </Reference>
       </ItemGroup>
     </When>
-    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.0' Or $(TargetFrameworkVersion) == 'v4.0.3' Or $(TargetFrameworkVersion) == 'v4.5' Or $(TargetFrameworkVersion) == 'v4.5.1' Or $(TargetFrameworkVersion) == 'v4.5.2' Or $(TargetFrameworkVersion) == 'v4.5.3' Or $(TargetFrameworkVersion) == 'v4.6' Or $(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2' Or $(TargetFrameworkVersion) == 'v4.6.3' Or $(TargetFrameworkVersion) == 'v4.7' Or $(TargetFrameworkVersion) == 'v4.7.1')" />
-    <When Condition="($(TargetFrameworkIdentifier) == '.NETCore') Or ($(TargetFrameworkIdentifier) == 'MonoAndroid' And ($(TargetFrameworkVersion) == 'v1.0' Or $(TargetFrameworkVersion) == 'v2.2' Or $(TargetFrameworkVersion) == 'v2.3' Or $(TargetFrameworkVersion) == 'v4.0.3' Or $(TargetFrameworkVersion) == 'v4.1' Or $(TargetFrameworkVersion) == 'v4.2' Or $(TargetFrameworkVersion) == 'v4.3' Or $(TargetFrameworkVersion) == 'v4.4' Or $(TargetFrameworkVersion) == 'v5.0' Or $(TargetFrameworkVersion) == 'v5.1' Or $(TargetFrameworkVersion) == 'v6.0' Or $(TargetFrameworkVersion) == 'v7.0' Or $(TargetFrameworkVersion) == 'v7.1' Or $(TargetFrameworkVersion) == 'v8.0')) Or ($(TargetFrameworkIdentifier) == 'MonoTouch') Or ($(TargetFrameworkIdentifier) == '.NETCoreApp' And ($(TargetFrameworkVersion) == 'v1.0' Or $(TargetFrameworkVersion) == 'v1.1' Or $(TargetFrameworkVersion) == 'v2.0')) Or ($(TargetFrameworkIdentifier) == '.NETStandard' And ($(TargetFrameworkVersion) == 'v1.1' Or $(TargetFrameworkVersion) == 'v1.2' Or $(TargetFrameworkVersion) == 'v1.3' Or $(TargetFrameworkVersion) == 'v1.4' Or $(TargetFrameworkVersion) == 'v1.5' Or $(TargetFrameworkVersion) == 'v1.6' Or $(TargetFrameworkVersion) == 'v2.0')) Or ($(TargetFrameworkProfile) == 'Profile7') Or ($(TargetFrameworkProfile) == 'Profile44') Or ($(TargetFrameworkIdentifier) == 'Xamarin.iOS') Or ($(TargetFrameworkIdentifier) == 'Xamarin.Mac') Or ($(TargetFrameworkIdentifier) == 'Xamarin.tvOS') Or ($(TargetFrameworkIdentifier) == 'Xamarin.watchOS')">
+    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.0' Or $(TargetFrameworkVersion) == 'v4.0.3' Or $(TargetFrameworkVersion) == 'v4.5' Or $(TargetFrameworkVersion) == 'v4.5.1' Or $(TargetFrameworkVersion) == 'v4.5.2' Or $(TargetFrameworkVersion) == 'v4.5.3' Or $(TargetFrameworkVersion) == 'v4.6' Or $(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2' Or $(TargetFrameworkVersion) == 'v4.6.3' Or $(TargetFrameworkVersion) == 'v4.7' Or $(TargetFrameworkVersion) == 'v4.7.1' Or $(TargetFrameworkVersion) == 'v4.7.2')">
+      <ItemGroup>
+        <Reference Include="FSharp.Core">
+          <HintPath>..\..\packages\FSharp.Core\lib\net40\FSharp.Core.dll</HintPath>
+          <Private>True</Private>
+          <Paket>True</Paket>
+        </Reference>
+      </ItemGroup>
+    </When>
+    <When Condition="($(TargetFrameworkIdentifier) == '.NETCore') Or ($(TargetFrameworkIdentifier) == 'MonoAndroid' And ($(TargetFrameworkVersion) == 'v1.0' Or $(TargetFrameworkVersion) == 'v2.2' Or $(TargetFrameworkVersion) == 'v2.3' Or $(TargetFrameworkVersion) == 'v4.0.3' Or $(TargetFrameworkVersion) == 'v4.1' Or $(TargetFrameworkVersion) == 'v4.2' Or $(TargetFrameworkVersion) == 'v4.3' Or $(TargetFrameworkVersion) == 'v4.4' Or $(TargetFrameworkVersion) == 'v5.0' Or $(TargetFrameworkVersion) == 'v5.1' Or $(TargetFrameworkVersion) == 'v6.0' Or $(TargetFrameworkVersion) == 'v7.0' Or $(TargetFrameworkVersion) == 'v7.1' Or $(TargetFrameworkVersion) == 'v8.0' Or $(TargetFrameworkVersion) == 'v8.1')) Or ($(TargetFrameworkIdentifier) == 'MonoTouch') Or ($(TargetFrameworkIdentifier) == '.NETCoreApp' And ($(TargetFrameworkVersion) == 'v1.0' Or $(TargetFrameworkVersion) == 'v1.1' Or $(TargetFrameworkVersion) == 'v2.0' Or $(TargetFrameworkVersion) == 'v2.1')) Or ($(TargetFrameworkIdentifier) == '.NETStandard' And ($(TargetFrameworkVersion) == 'v1.1' Or $(TargetFrameworkVersion) == 'v1.2' Or $(TargetFrameworkVersion) == 'v1.3' Or $(TargetFrameworkVersion) == 'v1.4' Or $(TargetFrameworkVersion) == 'v1.5' Or $(TargetFrameworkVersion) == 'v1.6' Or $(TargetFrameworkVersion) == 'v2.0')) Or ($(TargetFrameworkProfile) == 'Profile7') Or ($(TargetFrameworkProfile) == 'Profile44') Or ($(TargetFrameworkIdentifier) == 'Xamarin.iOS') Or ($(TargetFrameworkIdentifier) == 'Xamarin.Mac') Or ($(TargetFrameworkIdentifier) == 'Xamarin.tvOS') Or ($(TargetFrameworkIdentifier) == 'Xamarin.watchOS')">
       <ItemGroup>
         <Reference Include="FSharp.Core">
           <HintPath>..\..\packages\FSharp.Core\lib\portable-net45+netcore45\FSharp.Core.dll</HintPath>

src/CommandLine/CommandLine.csproj

@@ -14,6 +14,8 @@ namespace CommandLine.Core
 {
     static class ReflectionExtensions
     {
+        public const string CannotSetValueToTargetInstance = "Cannot set value to target instance.";
+
         public static IEnumerable<T> GetSpecifications<T>(this Type type, Func<PropertyInfo, T> selector)
         {
             return from pi in type.FlattenHierarchy().SelectMany(x => x.GetTypeInfo().GetProperties())
@@ -98,7 +100,7 @@ public static T SetProperties<T>(
         private static T SetValue<T>(this PropertyInfo property, T instance, object value)
         {
             Action<Exception> fail = inner => {
-                throw new InvalidOperationException("Cannot set value to target instance.", inner);
+                throw new InvalidOperationException(CannotSetValueToTargetInstance, inner);
             };
 
             try
@@ -123,6 +125,11 @@ private static T SetValue<T>(this PropertyInfo property, T instance, object valu
             {
                 fail(e);
             }
+            catch(ArgumentException e)
+            {
+                var argEx = new ArgumentException(InvalidAttributeConfigurationError.ErrorMessage, e);
+                fail(argEx);
+            }
 
             return instance;
         }

src/CommandLine/Core/ReflectionExtensions.cs

@@ -60,7 +60,11 @@ public enum ErrorType
         /// <summary>
         /// Value of <see cref="CommandLine.VersionRequestedError"/> type.
         /// </summary>
-        VersionRequestedError
+        VersionRequestedError,
+        /// <summary>
+        /// Value of <see cref="CommandLine.InvalidAttributeConfigurationError"/> type.
+        /// </summary>
+        InvalidAttributeConfigurationError
     }
 
     /// <summary>
@@ -471,4 +475,19 @@ internal VersionRequestedError()
         {
         }
     }
+
+
+    /// <summary>
+    /// Models an error generated when an invalid token is detected.
+    /// </summary>
+    public sealed class InvalidAttributeConfigurationError : Error
+    {
+        public const string ErrorMessage = "Check if Option or Value attribute values are set properly for the given type.";
+
+        internal InvalidAttributeConfigurationError()
+            : base(ErrorType.InvalidAttributeConfigurationError, true)
+        {
+        }
+    }
+
 }