Dynamic internals

Introductions  Alexandru Ghiondea  C# Compiler QA    What is your programming language of choice?  Do your apps interop with COM? Do you use dynamic languages?  Have you seen C# 4.0 before?

C# 4.0 language features  Named and Optional parameters  Omit “ref” for COM calls  noPIA  Co&Contra Variance  Dynamic

Why dynamic?  There is a lot of interest in accessing the highly dynamic object model of HTML DOM  COM is heavily used and the interop code could be easier to read and write  Dynamic languages are becoming increasingly popular  We need a unified way to work with all of the above

Architecture Python Binder Ruby Binder COM Binder JavaScript Binder Object Binder Dynamic Language Runtime Expression Trees Dynamic Dispatch Call Site Caching IronPythonIronRubyC#VB.NETOthers…

How dynamic works  We have a new type called dynamic  Calls on variables of type dynamic are treated differently by the compiler  We package extra information about the call  Calls can be: Method calls, property access, indexer call, operator call  There is a C# runtime binder to interpret the information (at runtime)  It uses the runtime type for all dynamic arguments  It uses the compile time type for all other arguments

CLR How dynamic works (2) Exe CompileRun Bind call Expression Tree Dynamic Call Delegate DLR Cache COM Binder IronPython Binder C# Runtime Binder …

IronPython, PowerPoint and C#

Under the cover  What is the Dynamic type?  There is no dynamic type. There is only object!  What operations are supported?  A variable of type dynamic is assumed to support any kind of operation (method call, property access, operator call and indexer call)  How is the information about the call stored?  Using CallSites objects the compiler packages data about the call

What does a CallSite contain?  Information about the call being made  What type of call (method call, property, operator, etc)  The name of the member  The context of the call  The type arguments for the call  Information about the parameters and return types  Is it a constant, is it passed by-ref, etc

Dynamic and CallSites

Dynamic FAQ  When do you go dynamic?  When the target of the call or any of it’s parameters are dynamic  What is the return type of a dynamic call?  It is dynamic in most cases*  *What about conversions and constructors?  They are dispatched at runtime, but their return type is known at compile time

Dynamic FAQ (2)  What about private methods?  Information about the context of call is embedded in the CallSite allowing the Binder to “do the right thing”  Calling a method off a non-dynamic target with dynamic arguments. (c.M(d));  It works as expected!  Can dynamic “cross” assembly boundaries?  Yes, we decorate any dynamic parameter or return type with a DynamicAttribute  It works for generic types constructed with dynamic as well

Dynamic FAQ (3)  Can I use Named and Optional with dynamic?  Yes!  And also Co & Contra variance  Where can’t I use dynamic?  Lambda expressions  LINQ  Can’t use dynamic and method groups  throw or catch statements

Return type, private methods and generics

Build you own dynamic object  It’s simple!  Implement IDynamicObject  Derive from DynamicObject  Implements IDynamicObject

I want to be dynamic!!!

 C# 4.0 Samples and Whitepaper   Visual C# Developer Center   C# team member’s blogs on dynamic     Additional Resources