community tech days c# 4.0

C# 4.0 Language Enhancements

Sankarsan Bose11th October 2009

Journey of C# Current Trends C# 4.0 Features Dynamic Objects Named And Optional Parameters Covariance And Contravariance Improved COM InterOp

Agenda

C#

C# 2.0

C# 3.0C# 4.0

Journey of C#

???

Static Language + Managed Code

Generics

Functional + LINQ

Current Trends

•Dynamic Typing•Dynamic Method DispatchDynamic

•Functions as first class objects•Focus on “WHAT” not “HOW”Functional

•Multi Core Computing•Message Based ConcurrencyConcurrent

C#

C# 4.0 Features

Dynamic Programming Optional and Named Parameters Co- and Contra-variance Improved COM Interoperability

Dynamic Programming

Ruby Code Sample

• No type is defined

• Stores string value

• “+” operator concatenates

• Assigned int values

• “+” operator adds

Type Determined At Runtime Based On Type Of Value Stored

Dynamic Programming

Ruby Code Sample

• Both classes define “print”

• Exactly same signature

• No type defined for parameter “p”

• Any object supporting method “print” is a valid input

•This is called “Duck Typing”

Method To Be Invoked Is Decided At Runtime

Dynamic Programming

Dynamic Method Dispatch in C# (Before 4.0)

Both are statically typed as IOfficeDocument

Dynamic ProgrammingDynamically Typed Objects in C# 4.0

• New keyword “dynamic” • Statically Typed as “dynamic”• Actual type determined at runtime

Dynamic Method Invocation

Dynamic Programming

Pros

No risk of brittle class hierarchy

Need not implement all methods of interface

More flexible , highly productive

Cons

Developer needs thorough understanding of codebase

Misuse might lead to poor maintainability

Dynamic Programming

Demo

Dynamic Programming

C# is a statically typed language

How we are making it dynamic ???

Here Comes DLR

Dynamic Language Runtime

Dynamic ProgrammingDLR is additional libraries to fit the dynamic languages into the CLR

• Store program/code as data

• Caching mechanism for dynamic call

• Provide language specific support

Dynamic ProgrammingClass Generated Under The Hood

• Compiler Generated Class• Reference to CallSite

• CallSite is created before method call

•Actual method call is delegated to CallSite

RuntimeCLR

DLR

Compile Time

Dynamic ProgrammingCLR – DLR Interaction

C# Source Code

MSIL CodeCompiler injects call to DLR CallSite

CallSite Cache

C# Runtime Binder

Call is delegated to DLR Call Site Cache

Call Runtime Binder for Cache miss

Determines type Determines methodReturns Expression Tree

Optional & Named Parameters

“b” & “c” are nullable & optional

Calling code has to pass null value

This is an issue for large no of parameters

Optional & Named Parameters

Solution Using Overload in C# (Before 4.0)

One overload accepts only “a”

Another accepts “a” & “b”

This is not possible

Signature clash with the previous method

Optional & Named Parameters

Optional Parameter with Default Value

Optional Parameter omitted in the call

Method call with parameter names

Position reversed

Solution Using C# 4.0

Optional & Named Parameters

Demo

Covariance & Contravariance

Ellipse

As per Liskov Substitution Principle(LSP):Any program which expects an object of EllipseWill function without any change with an object of Circle

CircleSubclass

Covariance – Type substitution as per LSP

Contravariance – Type substitution reverse to LSP

Covariance & Contravariance

Func<Base> is a delegate which returns type “Base”

Delegate Covariance in C# (Already Present)

Func<Base> can be replaced by function with return type “Derived”

Covariance & Contravariance

Func<Derived , Object> is a delegate which accepts type “Derived”

Delegate Contravariance in C# (Already Present)

Func<Base> can be replaced by function which accepts type “Base”

Covariance & Contravariance

Covariance in Arrays (Existing in C# )

This covariance is allowed

This code compiles

But throws Runtime Exception

Covariance & Contravariance

Invariance in Generic Types(Existing in C# )

This covariance is not allowed

This code will not compile

Before C# 4.0 Generic Types are Invariant

Covariance & Contravariance

Covariance in Generic Types of C# 4.0

This covariance is allowed

public interface IEnumerable<out T> : IEnumerable{

IEnumerator<T> GetEnumerator();}

Covariance & ContravarianceContravariance in Generic Types of C# 4.0

This Contravariance is allowed

public interface IComparer<in T>{

public int Compare(T left, T right);}

Covariance & Contravariance

Demo

Improved COM InterOp

Optional “ref” modifier

Optional and named parameters

Dynamic objects No additional type casts needed

InterOp type embedding (“No PIA”)

Improved COM InterOpPass Parameters without using “ref”

Improved COM InterOpTake advantage of named parameters & optional arguments

Improved COM InterOpTake advantage of named parameters & optional arguments

Improved COM InterOp

Demo

C#

C# 2.0

C# 3.0C# 4.0

Journey of C# - Revisited

Dynamic

Static Language + Managed Code

Generics

Functional + LINQ

Thank You

References

http://channel9.msdn.com/shows/Going+Deep/Inside-C-40-dynamic-type-optional-parameters-more-COM-friendly/

http://channel9.msdn.com/posts/Charles/C-40-Meet-the-Design-Team/

http://channel9.msdn.com/shows/Going+Deep/Expert-to-Expert-Anders-Hejlsberg-The-Future-of-C/

http://channel9.msdn.com/pdc2008/TL16/