.NET 4.0 Dynamic object used statically?

Question

I've asked another related question to this here: casting dynamic to static problem

I've gotten quite sick of XML configuration files in .NET and want to replace them with a format that is more sane. Therefore, I'm writing a config file parser for C# applications that will take a custom config file format, parse it, and create a Python source string that I can then execute in C# and use as a static object (yes that's right--I want a static (not the static type dyanamic) object in the end).

Here's an example of what my config file looks like:

// my custom config file format
GlobalName: ExampleApp

Properties
{
    ExternalServiceTimeout: "120"
}

Python 
{
    // this allows for straight python code to be added to handle custom config
    def MyCustomPython:
     return "cool"
}

Using ANTLR I've created a Lexer/Parser that will convert this format to a Python script. So assume I have that all right and can take the .config above and run my Lexer/Parser on it to get a Python script out the back (this has the added benefit of giving me a validation tool for my config). By running the resultant script in C#

// simplified example of getting the dynamic python object in C#
// (not how I really do it)
ScriptRuntime py = Python.CreateRuntime(); 
dynamic conf = py.UseFile("conftest.py");
dynamic t = conf.GetConfTest("test");

I can get a dynamic object that has my configuration settings. I can now get my config file settings in C# by invoking a dynamic method on that object:

//C# calling a method on the dynamic python object
var timeout = t.GetProperty("ExternalServiceTimeout");
//the config also allows for straight Python scripting (via the Python block)
var special = t.MyCustonPython();

of course, I have no type safety here and no intellisense support. I have a dynamic representation of my config file, but I want a static one. I know what my Python object's type is--it is actually newing up in instance of a C# class. But since it's happening in python, it's type is not the C# type, but dynamic instead. What I want to do is then cast the object back to the C# type that I know the object is:

// doesn't work--can't cast a dynamic to a static type (nulls out)
IConfigSettings staticTypeConfig = t as IConfigSettings

Is there any way to figure out how to cast the object to the static type? I'm rather doubtful that there is... so doubtful that I took another approach of which I'm not entirely sure about. I'm wondering if someone has a better way...

So here's my current tactic: since I know the type of the python object, I am creating a C# wrapper class:

public class ConfigSettings : IConfigSettings

that takes in a dynamic object in the ctor:

    public ConfigSettings(dynamic settings)
    {
        this.DynamicProxy = settings;
    }

    public dynamic DynamicProxy
    {
        get;
        private set;
    }

Now I have a reference to the Python dynamic object of which I know the type. So I can then just put wrappers around the Python methods that I know are there:

// wrapper access to the underlying dynamic object
// this makes my dynamic object appear 'static' 
public string GetSetting(string key)
{
    return this.DynamicProxy.GetProperty(key).ToString();
}

Now the dynamic object is accessed through this static proxy and thus can obviously be passed around in the static C# world via interface, etc:

// dependency inject the dynamic object around
IBusinessLogic logic = new BusinessLogic(IConfigSettings config);

This solution has the benefits of all the static typing stuff we know and love while at the same time giving me the option of 'bailing out' to dynamic too:

// the DynamicProxy property give direct access to the dynamic object
var result = config.DynamicProxy.MyCustomPython();

but, man, this seems rather convoluted way of getting to an object that is a static type in the first place! Since the whole dynamic/static interaction world is new to me, I'm really questioning if my solution is optimal or if I'm missing something (i.e. some way of casting that dynamic object to a known static type) about how to bridge the chasm between these two universes.

Sladen

This doesn't seem more sane than XML. Just saying... – Garlicky

I think you are getting the engine and the .config file itself confused... the .config file itself is quite a bit more sane IMHO. – Sladen

Answer 1

see the split off question here C# 4.0: casting dynamic to static that provides a way of making this work.

Sladen

Answer 2

If "IConfigSettings staticTypeConfig = t as IConfigSettings" isn't working then you don't actually have an object which is implementing IConfigSettings. Assuming you're declaring the class in Python you should make sure to include the interface in the base class list, for example:

class C(IConfigSettings):
   def SomeIConfigSettingsMember(self): pass

If that doesn't work then it might help if you post the Python code as well.

Populous

hmm. I don't get what I"m doing wrong. I just tried doing this with python newing up and returing a System.Uri object and I could cast it in C# to a System.Uri. But I can't get it to work with my own types. – Sladen

I split this off into another more specific question because I'm not getting this working: #2785752 – Sladen

Answer 3

The open source framework impromptu interface allows you to declare a static c# interface and a wrap any dynamic object.

Bestow