Dynamic binding in C# allows binding to occur at runtime rather than compile time. It is implemented using the Dynamic Language Runtime (DLR) which handles binding and execution. Dynamic binding is useful for accessing members with only a name at runtime, for interoperating with dynamic languages, and for letting an object decide how to handle calls. It has some restrictions like not supporting extension methods or resolving static members on dynamic types.

1. Buu Nguyen
DYNAMIC BINDING IN C#

2. Buu Nguyen
 Vice President of Technology, KMS Technology
 Lecturer, RMIT University Vietnam
 Microsoft MVP

3. Agenda
 What is dynamic binding
 How is it implemented
 When do we need it
 Restrictions of dynamic binding

4. What is Dynamic Binding

5. C# Language Evolution
C# 4.0
C# 3.0 Dynamic binding (*)
Named arguments
LINQ (*) Optional parameters
Auto- properties Generic variance
C# 2.0 Collection initializer Field-like events
Object initializer Robust locking
Generics (*) Anonymous types Better COM interop
Nullable types Extension methods
Anonymous methods Partial methods
C# 1.0 Yield return
Partial type
Lambda expressions
Expression trees
Static class
Namespace alias

6. Static vs. Dynamic Binding
Static Binding Dynamic Biding
 Compiler figures out which  All bindings happen during
members to call (binding run time
process)
 Defer subtype polymorphic
resolution till run time

7. Static Binding

8. Benefits of Static Binding
 Type and name errors are detected at
compile time, e.g.
 Invoke non-existent members
 Pass in arguments with wrong type
 Perform illegal cast

9. Dynamic Binding

10. How Is It Implemented?

11. Run Time Binding
 Instead of attempting binding and generating
CIL, the compiler packages the call and sends
it to the Dynamic Language Runtime
 At run time, the DLR performs binding and
execution

12. Under the Hood
becomes

13. The Dynamic Language Runtime

14. Process in a nutshell
C#
Dynamic builds
dynamic
Objects
User-defined or from other languages
compiled
uses IDynamicMetaObjectProvider
Call Sites
cached
Delegate
Expression emits
Tree
DLR
C# Binder builds

15. Dynamic Type in CIL

16. When Do We Need It?

17. Key Scenarios
1. Access a member with only knowledge of its
name, arguments, and target object
2. Interop with dynamic languages, e.g.
IronRuby, IronPython
3. Have the target object decide how to
respond to a call at run time

18. Key Scenarios
1. Access a member with only knowledge of its
name, arguments, and target object
2. Interop with dynamic languages, e.g.
IronRuby, IronPython
3. Have the target object decide how to
respond to a call at run time

19. Access Members

20. Reflection

21. Dynamic Type

22. Single vs. Multiple Dispatch
Single Dispatch Multiple Dispatch
 Method is selected based  Method is selected based
on the runtime type of the on both the runtime type
target object of the target object and
those of the method’s
arguments

23. Dispatch Example

24. Key Scenarios
1. Access a member with only knowledge of its
name, arguments, and target object
2. Interop with dynamic languages, e.g.
IronRuby, IronPython
3. Have the target object decide how to
respond to a call at run time

25. Invoke Ruby Code

26. Work with Ruby Class

27. Work with method_missing

28. Key Scenarios
1. Access a member with only knowledge of its
name, arguments, and target object
2. Interop with dynamic languages, e.g.
IronRuby, IronPython
3. Have the target object decide how to
respond to a call at run time

29. The Magic Interface
IDynamicMetaObjectProvider
ExpandoObject
DynamicObject

30. ExpandoObject

31. DynamicObject’s Operations
Name Description
TryGetMember Member getter, e.g. obj.Name
TrySetMember Member setter, e.g. obj.age = 10
TryDeleteMember Member removal (no equivalent in C#)
TryInvokeMember Method invocation, e.g. obj.Invoke()
TryConvert Casting, e.g. (int)obj
TryCreateInstance Object creation (no equivalent in C#)
TryInvoke Self invocation, e.g. obj(10)
TryBinaryOperation Binary operation, e.g. obj + 10
TryUnaryOperation Unary operation, e.g. !obj
TryGetIndex Indexer getter, e.g. obj[“key”]
TrySetIndex Indexer setter, e.g. obj[“key”] = value
TryDeleteIndex Indexer removal (no equivalent in C#)

32. Log Setters & Invocations

33. StaticInvoker

34. StaticInvoker

35. Close to the metal

36. …Close to the metal

37. …Close to the metal

38. Restrictions

39. Restriction #1
 Doesn’t work with extension methods

40. Restriction #2
 Can’t resolve static members or constructors
on a dynamic type

41. Restriction #3
 Method groups, anonymous methods and
lambda expressions to be casted to exact type

42. Restriction #4

43. Thank You!
buunguyen@kms-technology.com
http://vn.linkedin.com/in/buunguyen
http://www.twitter.com/buunguyen
http://www.facebook.com/buunguyen

44. References
 DLR specs from
http://dlr.codeplex.com/documentation
 C# in Depth, 2nd, Jon Skeet, Manning, 2010
 Pro DLR in .NET 4.0, Chaur Wu, Apress, 2010