C# 8.0 in a Nutshell

Chapter 20. Dynamic Programming

Chapter 4 explained how dynamic binding works in the C# language. In this chapter, we look briefly at the Dynamic Language Runtime and then explore the following dynamic programming patterns:

• Numeric type unification

• Dynamic member overload resolution

• Custom binding (implementing dynamic objects)

• Dynamic language interoperability

Note

In Chapter 25, we describe how dynamic can improve COM interoperability.

The types in this chapter reside in the System.Dynamic namespace, except for CallSite<>, which resides in System.Runtime.CompilerServices.

The Dynamic Language Runtime

C# relies on the Dynamic Language Runtime (DLR) to perform dynamic binding.

Contrary to its name, the DLR is not a dynamic version of the CLR. Rather, it’s a library that sits atop the CLR—just like any other library such as System.Xml.dll. Its primary role is to provide runtime services to unify dynamic programming—in both statically and dynamically typed languages. Hence, languages such as C#, Visual Basic, IronPython, and IronRuby all use the same protocol for calling functions dynamically. This allows them to share libraries and call code written in other languages.

What Are Call Sites?

When the compiler encounters a dynamic expression, it has no idea who will evaluate that expression at runtime. For instance, consider the following method:

public dynamic Foo (dynamic x, dynamic y)
{
  return x / y;   // Dynamic expression
}

The x and y variables could be any CLR object, ...