Let DynamicObect's TryGetMember and TrySetMember return a class in C#

Question

I have a class inheriting from DynamicObject
In this class I have a TryGetMember that I try to evaluate to a static class.

How can TryGetMember overriden from DynamicObject result in a static class?

TL;DR

Calling code:

dynamic sut = new ReachIn();
sut.myclass.MyInnerStaticClass.MyProperty= "fortytwo";

My DynamicObject class tries to return myclass as the MyClass instance.

internal class ReachIn : DynamicObject
{
    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = MyClass; // Does not compile.
        return true;
     }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        value = MyClass // Does not compile;
        return true;
    }
}

and what is returned is here:

internal class MyClass
{
    internal static class MyInnerStaticClass
    {
        public static string MyProperty { get; set; }
    }
}

This example is a bit forced. It is just a very simplified example of a dynamic object making private fields, properties, methods (and (not yet) classes) visible for testing purpose. I also know one should not write tests this way but I have an esoteric reason. or because I can.

I don´t fully understand what you want to return when calling `sut.myclass`. Should this implicitely create an instance of whatever the type of that property is? Basically a `DynamicObject` is just a dictionary. It does not *create* instances, it only makes *accessing* them dynamic. — MakePeaceGreatAgain, Apr 12 '18 at 19:25
@HimBromBeere My example is forced. In my real code `myclass` in `sut.myclass` means something and would fail. In hindsight I should have called `myclass` for `Anything`. In my example I did not want to convolute the question with (lots of) reflection code; instead it just *tries to* return a static class. — LosManos, Apr 13 '18 at 07:14

arekzyla · Accepted Answer · 2018-04-12T21:07:39.723

Regardless of your class design I am going to show that what you are trying to achieve is possible with dynamic types and reflection. Firstly a dynamic object is just an object that can take some string name in method like TryGetMember to perform some action. Secondly with string names and reflection you can perform any operation on your objects. So simple dynamic object implementation that will work with your example looks like this:

internal class ReachIn : DynamicObject
{
    private readonly Type type;

    private readonly string @namespace;

    public ReachIn(Type type = null, string @namespace = null)
    {
        this.type = type;
        this.@namespace = @namespace;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        if (type == null)
        {
            result = new ReachIn(Type.GetType($"{@namespace}.{binder.Name}".Trim('.')));
            return true;
        }

        var member = type.GetMember(binder.Name).Single(); 

        if (member.MemberType == MemberTypes.NestedType)
        {
            result = new ReachIn((Type)member);
        }
        else if (member.MemberType == MemberTypes.Property)
        {
            result = ((PropertyInfo)member).GetValue(null);
        }
        else
        {
            result = null;
            return false;
        }

        return true;
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        var member = type.GetMember(binder.Name).Single();

        if (member.MemberType == MemberTypes.Property)
        {
            ((PropertyInfo)member).SetValue(null, value);

            return true;
        }

        return false;
    }
}

So it will work for a sample class with public modifiers:

public class MyClass
{
    public static class MyInnerStaticClass
    {
        public static string MyProperty { get; set; }
    }
}

With this you can set your static property like:

 dynamic sut = new ReachIn(@namespace: "ConsoleApp8");
 sut.MyClass.MyInnerStaticClass.MyProperty = "safd";

It's tested only with your example so for other cases you would need to provide some additional implementation. Not to mention the performance of it would be very bad because of reflection.

Let DynamicObect's TryGetMember and TrySetMember return a class in C#

1 Answers1