Dynamic Binding in C# 4.0

DYNAMIC BINDING IN C# Buu Nguyen

Buu Nguyen

Vice President of Technology, KMS Technology

Lecturer, RMIT University Vietnam

Microsoft MVP

Agenda

What is dynamic binding

How is it implemented

When do we need it

Restrictions of dynamic binding

What is Dynamic Binding

C# Language Evolution

C# 1.0

C# 2.0

C# 3.0

C# 4.0

Generics (*) Nullable types Anonymous methods Yield return Partial type Static class Namespace alias

LINQ (*) Auto- properties Collection initializer Object initializer Anonymous types Extension methods Partial methods Lambda expressions Expression trees

Dynamic binding (*) Named arguments Optional parameters Generic variance Field-like events Robust locking Better COM interop

Static vs. Dynamic Binding

Static Binding Dynamic Biding

Compiler figures out which members to call (binding process) Defer subtype polymorphic

resolution till run time

All bindings happen during run time

Static Binding

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

Dynamic Binding

How Is It Implemented?

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

Under the Hood

becomes

The Dynamic Language Runtime

Process in a nutshell

C# dynamic

Call Sites

C# Binder

Expression Tree

Delegate

Dynamic Objects

compiled

builds

emits

DLR

uses

builds

cached

User-defined or from other languages

IDynamicMetaObjectProvider

Dynamic Type in CIL

When Do We Need It?

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

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

Access Members

Reflection

Dynamic Type

Single vs. Multiple Dispatch

Single Dispatch Multiple Dispatch

Method is selected based on the runtime type of the target object

Method is selected based on both the runtime type of the target object and those of the method’s arguments

Dispatch Example

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

Invoke Ruby Code

Work with Ruby Class

Work with method_missing

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

The Magic Interface

IDynamicMetaObjectProvider

DynamicObject

ExpandoObject

ExpandoObject

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#)

Log Setters & Invocations

StaticInvoker

StaticInvoker

Close to the metal

…Close to the metal

…Close to the metal

Restrictions

Restriction #1

Doesn’t work with extension methods

Restriction #2

Can’t resolve static members or constructors on a dynamic type

Restriction #3

Method groups, anonymous methods and lambda expressions to be casted to exact type

Restriction #4

Thank You!

[email protected]

http://vn.linkedin.com/in/buunguyen

http://www.twitter.com/buunguyen

http://www.facebook.com/buunguyen

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