Passing anonymous type as method parameters

Question

In my plugin architecture I am currently passing a plugin name (string), method name (string) and parameters (object array) to my plugin service to execute the specified method and return the result (of type T).

The plugin service's execute method can be seen below:

public TResult Execute<TResult>(string pluginName, string operation, params object[] input) {
    MethodInfo method = null;
    TResult result = default(TResult);

    var plugin = _plugins.Enabled().FirstOrDefault(x => x.GetType().Name.Equals(pluginName,  StringComparison.InvariantCultureIgnoreCase));

    if (plugin != null) {
        method = plugin.GetType().GetMethods().FirstOrDefault(x => x.Name == operation);
        if (method != null) {
            result = (TResult)method.Invoke(plugin, input);
        }
    }
    return result;
  }

An example usage:

var url = AppHelper.PluginService.Execute<string>(
    "ImagePlugin",
    "GetImageUrl",
    new object[] { image, size });

What I would rather do is pass in an anonymous type instead (as I think this is more readable) i.e.

var url = AppHelper.PluginService.Execute<string>(
    "ImagePlugin",
    "GetImageUrl",
    new { image = image, targetSize = size });

How would I change my Execute method to map the anonymous type properties to my plugin method parameters?

I had considered using the new dynamic type in .net 4.0 but I prefer to define my parameters on the plugin method rather than accepting one dynamic object.

Thanks Ben

[Update]

After looking through the ASP.NET MVC source code it seems simple enough to pull the anonymous type into an object dictionary e.g. RouteValueDictionary. With the help of reflection a linq expression is created dynamically. Although its a good implementation, I didn't really want all this extra complexity.

As per the comment below, I can achieve readability just by specifying my parameters inline (no need for the object array declaration):

var url = AppHelper.PluginService.Execute<string>("ImagePlugin", "GetImageUrl", image, size);

Answer 1

I did eventually come across this post that demonstrates using anonymous types as dictionaries. Using this method you could pass the anonymous type as a method parameter (object) and access it's properties.

However, I would also add that after looking into the new dynamic features in .net 4.0 such as the ExpandoObject, it feels much cleaner to pass a dynamic object as a parameter:

        dynamic myobj = new ExpandoObject();         myobj.FirstName = "John";         myobj.LastName = "Smith";          SayHello(myobj);         ...........          public static void SayHello(dynamic properties)         {            Console.WriteLine(properties.FirstName + " " + properties.LastName);         } 

Answer 2

Use dynamic object for parameters if you want to pass an anonymous type. The execute method of a plugin should expect certain properties of a parameter object in order to work. By using dynamic keyword C# compiler will be instructed to not perform type check on a parameter and will allow to use strongly-typed syntax in the plugin code. The properties name resolution will happen in run-time and if a passed object did not have such properties an exception will be thrown.

var o = new { FirstName = "John", LastName = "Doe" };

var result = MyMethod(o);

string MyMethod(dynamic o)
{
    return o.FirstName + " " + o.LastName;
}

Read more in this blog post

Answer 3

There are some ways to make this possible although I wouldn't advice any of them.

First, you can use reflection which means you have to write a lot of additional (error-prone) code in your PluginService.Execute method to get the values you want.

Second, if you know the parameters of the anonymous type you are passing to your method you can use the technique described here. You can cast to another anonymous type inside your method that has the same properties. Here is another description of the same technique from Jon Skeet.

Third, you can use classes from the System.ComponentModel. For example, ASP.NET MVC uses this. It uses reflection under the hood. However, in ASP.NET MVC either the property names are well-known (controller and action for example) or their names don't matter because they are passed as-is to a controller method (id for example).