Inheritance of Attributes from Interface Members

[bepursuant]

Hello team - This might be an easy one to put to rest, I think I just need a castle expert to look at it.

I have an issue with a separate project, and I think it comes down to something in the Castle proxy generation.

The root of the question is - can Castle allow my generated proxy to inherit attributes from its source Interface? The linked issue has an example project demonstrating the disconnect.

[stakx]

Hi @bepursuant. I don't remember all the implementation details without looking them up, but off the top of my head:

As a rule of thumb, DynamicProxy only replicates non-inherited custom attributes. There is currently no mechanism or option to change that behavior. The only thing you can do is globally specify (via AttributesToAvoidReplicating) custom attribute types that should not get replicated... but that is the exact opposite of what you need.

DescriptionAttributes will not get replicated because they are inherited. Let's check its definition:

[AttributeUsage(AttributeTargets.All)]
public class DescriptionAttribute : Attribute

Its [AttributeUsage] does not explicitly specify Inherited = false, so the default (Inherited = true) applies.

Knowing this, you could try subclassing DescriptionAttribute and then reapply [AttributeUsage] with Inherited = false. If you then use that custom attribute type, DynamicProxy should replicate it on the generated proxy type.

Let's try this:

using System;
using System.ComponentModel;
using System.Reflection;

using Castle.DynamicProxy;

var generator = new ProxyGenerator();

var foo = generator.CreateInterfaceProxyWithoutTarget<IFoo>();
var fooAttr = foo.GetType().GetProperty("Property").GetCustomAttribute<DescriptionAttribute>();
Console.WriteLine(fooAttr?.Description);  // => no output because attribute is not there

var bar = generator.CreateInterfaceProxyWithoutTarget<IBar>();
var barAttr = bar.GetType().GetProperty("Property").GetCustomAttribute<DescriptionAttribute>();
Console.WriteLine(barAttr?.Description);  // => outputs "Some description"

public interface IFoo
{
    [Description("Some description")]
    object Property { get; set; }
}

public interface IBar
{
    [NonInheritedDescription("Some description")]
    object Property { get; set; }
}

[AttributeUsage(AttributeTargets.All, Inherited = false)]
public class NonInheritedDescriptionAttribute : DescriptionAttribute
{
    public NonInheritedDescriptionAttribute(string description) : base(description) { }
}

Not sure if this will help in your situation, but it may be worth a shot.

[stakx]

@bepursuant: has the above post answered your question? (If so, let's close this issue.)

[bepursuant]

@stakx - thanks so much for the thorough explanation and example resolution. This exactly solved my dilemma, with only three lines of code! Really appreciate the help! I've added the details to my original issue in the aloneguid/config project for anyone else looking at a similar issue.