devLink - What's New in C# 4?

What’s new in C# 4?Kevin Pilch-Bisson

kevinpi@microsoft.com

http://twitter.com/Pilchie

The Evolution of C#

C# 1.0

C# 2.0

C# 3.0

Managed Code

Generics

Language Integrated Query

Trends

The Evolution of C#

C# 1.0

C# 2.0

C# 3.0

Managed Code

Generics

Language Integrated Query

C# 4.0Dynamic Programming

C# 4.0 Language Innovations

PythonBinder

RubyBinder

COMBinder

JavaScriptBinder

ObjectBinder

.NET Dynamic Programming

Dynamic Language Runtime

Expression Trees Dynamic Dispatch Call Site Caching

IronPython IronRuby C# VB.NET Others…

Dynamically Typed Objects

Cal cul at or cal c = Get Cal cul at or( ) ;i nt sum = cal c. Add( 10, 20) ;

obj ect cal c = Get Cal cul at or( ) ;Type cal cType = cal c. Get Type( ) ;obj ect res = cal cType. I nvokeMember( " Add" , Bi ndi ngFl ags. I nvokeMet hod, nul l , new obj ect [ ] { 10, 20 } ) ;i nt sum = Convert . ToI nt 32( res) ;

Scr i pt Obj ect cal c = Get Cal cul at or( ) ;obj ect res = cal c. I nvoke( " Add" , 10, 20) ;i nt sum = Convert . ToI nt 32( res) ;

dynami c cal c = Get Cal cul at or( ) ;i nt sum = cal c. Add( 10, 20) ;

Statically typed to be dynamic

Dynamic method invocation

Dynamic conversion

Dynamically Typed Objects

dynami c cal c = Get Cal cul at or( ) ;dynami c sum = cal c. Add( 10, 20) ;

Another word for System.Object…

When operand(s) are dynamic…• Member selection deferred to run-time• Dispatch through COM, object itself, or C# binder• Run-time type(s) substituted for dynamic• Compile-time type of operation is dynamic

…but with dynamic semantics

Dynamically Typed Objects

publ i c st at i c cl ass Mat h{ publ i c st at i c deci mal Abs(deci mal val ue) ; publ i c st at i c doubl e Abs(doubl e val ue) ; publ i c st at i c f l oat Abs( f l oat val ue) ; publ i c st at i c i nt Abs( i nt val ue) ; publ i c st at i c l ong Abs( l ong val ue) ; publ i c st at i c sbyt e Abs(sbyt e val ue) ; publ i c st at i c short Abs(short val ue) ; . . .}

doubl e x = 1. 75;doubl e y = Mat h. Abs(x) ;

dynami c x = 1. 75;dynami c y = Mat h. Abs(x) ;

dynami c x = 2;dynami c y = Mat h. Abs(x) ;

Method chosen at compile-time:

double Abs(double x)

Method chosen atrun-time:

double Abs(double x)

Method chosen atrun-time:

int Abs(int x)

Dynamically Typed Objects

dynami c d = Get Dynami cObj ect ( . . . ) ;

d. Foo( 10, " Hel l o" ) ; / / Met hod i nvocat i on

i nt si ze = d. Wi dt h; / / Propert y access

d. x = 25; / / Fi el d access

d[ " one" ] = d[ " t wo" ] ; / / I ndexer access

i nt i = d + 3; / / Operat or appl i cat i on

st r i ng s = d(5, 10) ; / / Del egat e i nvocat i on

Dynamically Typed Objects

Optional and Named Parameters

publ i c St reamReader OpenText Fi l e( st r i ng pat h, Encodi ng encodi ng, bool det ect Encodi ng, i nt buf f erSi ze) ;

publ i c St reamReader OpenText Fi l e( st r i ng pat h, Encodi ng encodi ng, bool det ect Encodi ng) ;

publ i c St reamReader OpenText Fi l e( st r i ng pat h, Encodi ng encodi ng) ;

publ i c St reamReader OpenText Fi l e( st r i ng pat h) ;

Primary method

Secondary overloads

Call primary with default values

Optional and Named Parameters

publ i c St reamReader OpenText Fi l e( st r i ng pat h, Encodi ng encodi ng, bool det ect Encodi ng, i nt buf f erSi ze) ;

publ i c St reamReader OpenText Fi l e( st r i ng pat h, Encodi ng encodi ng = nul l , bool det ect Encodi ng = t rue, i nt buf f erSi ze = 1024) ;

Optional parameters

OpenText Fi l e( " f oo. t xt " , Encodi ng. UTF8) ;OpenText Fi l e( " f oo. t xt " , Encodi ng. UTF8, buf f erSi ze: 4096) ;

Named argument

OpenText Fi l e( buf f erSi ze: 4096, pat h: " f oo. t xt " , det ect Encodi ng: f al se) ;

Named arguments must be last

Non-optional must be specified

Evaluated inorder written

Named arguments can be in any order

Improved COM Interoperability

obj ect f i l eName = " Test . docx" ;obj ect mi ssi ng = Syst em. Ref l ect i on. Mi ssi ng. Val ue;

doc. SaveAs( ref f i l eName, ref mi ssi ng,  ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng, ref mi ssi ng) ;

doc. SaveAs( " Test . docx" ) ;

Improved COM Interoperability

• Automatic object dynamic mapping• Optional and named parameters• Indexed properties• Optional “ref” modifier• Interop type embedding (“No PIA”)

Improved COM Interoperability

Co- and Contra-variance

voi d Process(obj ect [ ] obj ect s) { … }

st r i ng[ ] st r i ngs = Get St r i ngArray( ) ;Process(st r i ngs) ;

voi d Process(obj ect [ ] obj ect s) { obj ect s[0] = " Hel l o" ; / / Ok obj ect s[ 1] = new But t on( ) ; / / Except i on!}

Li st <st r i ng> st r i ngs = Get St r i ngLi st ( ) ;Process(st r i ngs) ;

voi d Process( I Enumerabl e<obj ect > obj ect s) { … }

.NET arrays are co-variant

…but not safelyco-variant

Until now, C# generics have been invariant

voi d Process( I Enumerabl e<obj ect > obj ect s) { / / I Enumerabl e<T> i s read-onl y and / / t heref ore saf el y co-var i ant}

C# 4.0 supports safe co- and

contra-variance

Safe Co- and Contra-variance

publ i c i nt er f ace I Enumerabl e<T>{ I Enumerat or<T> Get Enumerat or( ) ;}

publ i c i nt er f ace I Enumerat or<T>{ T Current { get ; } bool MoveNext ( ) ;}

publ i c i nt er f ace I Enumerabl e<out T>{ I Enumerat or<T> Get Enumerat or( ) ;}

publ i c i nt er f ace I Enumerat or<out T>{ T Current { get ; } bool MoveNext ( ) ;}

out = Co-variantOutput positions only

I Enumerabl e<st r i ng> st r i ngs = Get St r i ngs( ) ;I Enumerabl e<obj ect > obj ect s = st r i ngs;

Can be treated asless derived

publ i c i nt er f ace I Comparer<T>{ i nt Compare(T x, T y) ;}

publ i c i nt er f ace I Comparer<i n T>{ i nt Compare(T x, T y) ;}

I Comparer<obj ect > obj Comp = Get Comparer( ) ;I Comparer<st r i ng> st rComp = obj Comp;

in = Contra-variantInput positions only

Can be treated asmore derived

Variance in C# 4.0

• Supported for interface and delegate types• “Statically checked definition-site variance”• Value types are always invariant

• IEnumerable<int> is not IEnumerable<object>• Similar to existing rules for arrays

• ref and out parameters need invariant type

Variance in .NET Framework 4.0

System.Collections.Generic.IEnumerable<out T>System.Collections.Generic.IEnumerable<out T>

System.Collections.Generic.IEnumerator<out T>System.Collections.Generic.IEnumerator<out T>

System.Linq.IQueryable<out T>System.Linq.IQueryable<out T>

System.Collections.Generic.IComparer<in T>System.Collections.Generic.IComparer<in T>

System.Collections.Generic.IEqualityComparer<in T>System.Collections.Generic.IEqualityComparer<in T>

System.IComparable<in T>System.IComparable<in T>

InterfacesInterfaces

System.Func<in T, …, out R>System.Func<in T, …, out R>

System.Action<in T, …>System.Action<in T, …>

System.Predicate<in T>System.Predicate<in T>

System.Comparison<in T>System.Comparison<in T>

System.EventHandler<in T>System.EventHandler<in T>

DelegatesDelegates

The Evolution of C#

C# 1.0

C# 2.0

C# 3.0

Managed Code

Generics

Language Integrated Query

C# 4.0Dynamic Programming

Compiler as a Service

CompilerCompilerSource code

Source code

SourceFile

Source codeSource code

.NET Assembly

Class

Field

public Foo

private

string

X

Meta-programming Read-Eval-Print Loop

LanguageObject Model

DSL Embedding

Compiler as a Service

Questions?

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