Correct way to construct .NET Expression to invoke dynamic objects

Question

I need to create a System.Linq.Expressions.Expression that call a dynamic object. The dynamic object can be an ExpandoObject or any other IDynamicMetaObjectProvider.

Consider the following test:

var myInstance = DateTime.Now;

var methodInfo = myInstance.GetType().GetMethod("ToUniversalTime");

var methodCallExpression = Expression.Call(Expression.Constant(myInstance), methodInfo);
var expression = Expression.Lambda(methodCallExpression);

Assert.AreEqual(myInstance.ToUniversalTime(), expression.Compile().DynamicInvoke());

I need to create an equivalent expression when myInstance is declared like (just as an example):

dynamic myInstance = new ExpandoObject();
myInstance.MyMethod = new Func<string>(() => "hello world");

I suppose that I need to use Expression.Dynamic method (see MSDN). But I don't known how to use it. I have tried to search on google but the only examples that I have found use the Microsoft.CSharp.RuntimeBinder.Binder class (see MSDN) that cannot be officially used:

This API supports the .NET Framework infrastructure and is not intended to be used directly from your code.

Using Microsoft.CSharp.RuntimeBinder.Binder I can write the code below:

dynamic myInstance = new ExpandoObject();
myInstance.MyMethod = new Func<string>(() => "hello world");

var binder = Binder.InvokeMember(
    CSharpBinderFlags.None,
    "MyMethod",
    null,
    this.GetType(),
    new[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.Constant, null) });

var methodCallExpression = Expression.Dynamic(binder, typeof(object), Expression.Constant(myInstance));
var expression = Expression.Lambda(methodCallExpression);

Assert.AreEqual(myInstance.MyMethod(), expression.Compile().DynamicInvoke());

It this solution correct?

Answer 1

Here is the catch: from my understanding, there is no meaning in making a dynamic call without some kind of Binder object.

The binder object represents the rules that are followed for dynamic name resolution:

• Should the match be case-sensitive?
• How should method overloads be resolved?
• What to do if the object is a non-dynamic object?
• What fallbacks do you use?

In other words, the Binder object represents the semantics of the calling "language", while IDynamicMetaObjectProvider represents the semantics of the called object.

So, yes, we are not supposed to use the CSharp Binder object. That can be felt especially when some issues happen that can only be worked around by using the object's internals. However, the alternative is simply to use another, non-framework-provided, Binder implementation.