C# in Depth

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Fast-tracked delegatesThis chapter covers■■■■■Longwinded C# 1 syntaxSimplified delegate constructionCovariance and contravarianceAnonymous methodsCaptured variablesThe journey of delegates in C# and .NET is an interesting one, showing remarkableforesight (or really good luck) on the part of the designers. The conventions suggestedfor event handlers in .NET 1.0/1.1 didn’t make an awful lot of sense—untilC# 2 showed up. Likewise, the effort put into delegates for C# 2 seems in some waysout of proportion to how widely used they are—until you see how pervasive theyare in idiomatic C# 3 code. In other words, it’s as if the language and platformdesigners had a vision of at least the rough direction they would be taking, yearsbefore the destination itself became clear.Of course, C# 3 is not a “final destination” in itself, and we may be seeing furtheradvances for delegates in the future—but the differences between C# 1 andC# 3 in this area are startling. (The primary change in C# 3 supporting delegates isin lambda expressions, which we’ll meet in chapter 9.)137Licensed to Rhona Hadida
138 CHAPTER 5 Fast-tracked delegatesC# 2 is a sort of stepping stone in terms of delegates. Its new features pave the wayfor the even more dramatic changes of C# 3, keeping developers reasonably comfortablewhile still providing useful benefits. The extent to which this was a finely balancedact as opposed to intuition and a following wind is likely to stay unknown, butwe can certainly reap the benefits.Delegates play a more prominent part in .NET 2.0 than in earlier versions,although they’re not as common as they are in .NET 3.5. In chapter 3 we saw how theycan be used to convert from a list of one type to a list of another type, and way back inchapter 1 we sorted a list of products using the Comparison delegate instead of theIComparer interface. Although the framework and C# keep a respectful distance fromeach other where possible, I believe that the language and platform drove each otherhere: the inclusion of more delegate-based API calls supported the improved syntaxavailable in C# 2, and vice versa.In this chapter we’ll see how C# 2 makes two small changes that make life easierwhen creating delegate instances from normal methods, and then we’ll look at thebiggest change: anonymous methods, which allow you to specify a delegate instance’saction inline at the point of its creation. The largest section of the chapter is devotedto the most complicated part of anonymous methods, captured variables, which providedelegate instances with a richer environment to play in. We’ll cover the topic insignificant detail due to its importance and complexity.First, though, let’s remind ourselves of the pain points of C# 1’s delegate facilities.5.1 Saying goodbye to awkward delegate syntaxThe syntax for delegates in C# 1 doesn’t sound too bad—the language already has syntacticsugar around Delegate.Combine, Delegate.Remove, and the invocation of delegateinstances. It makes sense to specify the delegate type when creating a delegateinstance—it’s the same syntax used to create instances of other types, after all.This is all true, but for some reason it also sucks. It’s hard to say exactly why the delegatecreation expressions of C# 1 raise hackles, but they do—at least for me. Whenhooking up a bunch of event handlers, it just looks ugly to have to write “newEventHandler” (or whatever is required) all over the place, when the event itself hasspecified which delegate type it will use. Beauty is in the eye of the beholder, of course,and you could argue that there’s less call for guesswork when reading event handler wiringcode in the C# 1 style, but the extra text just gets in the way and distracts from theimportant part of the code: which method you want to handle the event.Life becomes a bit more black and white when you consider covariance and contravarianceas applied to delegates. Suppose you’ve got an event handling methodthat saves the current document, or just logs that it’s been called, or any number ofother actions that may well not need to know details of the event. The event itselfshouldn’t mind that your method is capable of working with only the information providedby the EventHandler signature, even though it is declared to pass in mouseevent details. Unfortunately, in C# 1 you have to have a different method for each differentevent handler signature.Licensed to Rhona Hadida
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C# in DepthLicensed to Rhona Hadida
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C# in DepthJON SKEETMANNINGGreenwic
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Licensed to Rhona Hadida
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Licensed to Rhona Hadida
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xCONTENTS1.3 The .NET platform 24Di
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xiiCONTENTS5.4 Inline delegate acti
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xivCONTENTS9.4 Changes to type infe
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xviCONTENTS13.2 Delegation as the n
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xviiiFOREWORDOf the latter kind, th
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xxPREFACEdidn’t start using C#2 u
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xxiiACKNOWLEDGMENTSThe aforemention
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xxivABOUT THIS BOOKwant to become e
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xxviABOUT THIS BOOKSQL statements.
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about the cover illustrationThe cap
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xxxCOMMENTS FROM THE TECH REVIEWThi
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Chapter 1 presents a bird’s-eye v
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4 CHAPTER 1 The changing face of C#
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10 CHAPTER 1 The changing face of C
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Core foundations:building on C# 1Th
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34 CHAPTER 2 Core foundations: buil
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C# 2 and 3: new features on a solid
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C# 2 and 3: new features on a solid
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Summary59Listing 2.7 shows a number
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Part 2C#2:solving the issuesof C#1I
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Parameterizedtyping with genericsTh
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Simple generics for everyday use65o
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Simple generics for everyday use67I
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Simple generics for everyday use69t
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Simple generics for everyday use71N
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Simple generics for everyday use73}
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Beyond the basics75parameters. You
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Beyond the basics77NOTEC# vs. CLI s
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Beyond the basics79combined togethe
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Beyond the basics813.3.3 Implementi
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Beyond the basics83derive from a pa
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Advanced generics85implement IEquat
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Page 122 and 123: Advanced generics91}{}return new Co
Page 124 and 125: Advanced generics93Listing 3.10Usin
Page 126 and 127: Advanced generics95REFLECTING GENER
Page 128 and 129: Generic collection classes in .NET
Page 134 and 135: Limitations of generics in C# and o
Page 142 and 143: Summary111My personal opinion is th
Page 144 and 145: What do you do when you just don’
Page 146 and 147: System.Nullable and System.Nullable
Page 152 and 153: C# 2’s syntactic sugar for nullab
Page 162 and 163: Novel uses of nullable types131part
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Page 166 and 167: Novel uses of nullable types135}{}i
Page 170 and 171: Saying goodbye to awkward delegate
Page 172 and 173: Covariance and contravariance141met
Page 174 and 175: Covariance and contravariance143som
Page 176 and 177: Inline delegate actions with anonym
Page 182 and 183: Capturing variables in anonymous me
Page 192 and 193: Implementingiterators the easy wayT
Page 194 and 195: C# 1: the pain of handwritten itera
Page 196 and 197: C# 2: simple iterators with yield s
Page 204 and 205: Real-life example: iterating over r
Page 210 and 211: Pseudo-synchronous code with the Co
Page 212 and 213: Summary181(without using a dedicate
Page 214 and 215: Concluding C# 2:the final featuresT
Page 216 and 217: Partial types185C# 2 allows more th
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Partial types187code generator can
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Partial types189Listing 7.2A partia
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Static classes191}public static str
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Namespace aliases193same syntax is
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Namespace aliases195Listing 7.6usin
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Pragma directives197}}Console.Write
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Fixed-size buffers in unsafe code19
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Exposing internal members to select
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Exposing internal members to select
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Part 3C# 3—revolutionizinghow we
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Cutting fluffwith a smart compilerT
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Automatically implemented propertie
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Implicit typing of local variables2
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Implicit typing of local variables2
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Simplified initialization215simple
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Simplified initialization217The par
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Simplified initialization219CREATIN
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Simplified initialization221Home =
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Implicitly typed arrays2238.4 Impli
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Anonymous types225new { Name = "Hol
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Anonymous types227That certainly wo
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Summary229typed local variables—a
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Lambda expressions and expression t
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Lambda expressions as delegates233L
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Simple examples using List and even
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Simple examples using List and even
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Expression trees239code to run on y
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Expression trees241So, what’s the
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Expression trees243the tree and how
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Changes to type inference and overl
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Summary253find the better conversio
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Extension methodsThis chapter cover
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Life before extension methods257Sys
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Extension method syntax259extension
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Extension method syntax26110.2.3 Ho
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Extension methods in .NET 3.5263pub
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Extension methods in .NET 3.5265ret
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Extension methods in .NET 3.5267as
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Extension methods in .NET 3.5269Now
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Usage ideas and guidelines271extens
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Usage ideas and guidelines273those
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Query expressionsand LINQ to Object
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Introducing LINQ277the extension me
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Introducing LINQ279Figure 11.1 show
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Introducing LINQ281flexible. In par
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Simple beginnings: selecting elemen
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Filtering and ordering a sequence29
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Filtering and ordering a sequence29
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Let clauses and transparent identif
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Joins29711.5 JoinsEach part of the
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Joins299from defect inSampleData.Al
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Joins30111.5.2 Group joins with joi
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Joins303foreach (var grouped in que
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Joins305from user inSampleData.AllU
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Groupings and continuations307In ju
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Groupings and continuations309from
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Groupings and continuations311perso
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Summary31311.7 SummaryIn this chapt
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LINQ to SQL315LINQ to DataSet and L
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LINQ to SQL317■ I changed the typ
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LINQ to SQL319each of type Table fo
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LINQ to SQL321FROM [dbo].[Defect] A
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LINQ to SQL323FROM [dbo].[Notificat
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LINQ to SQL325using (var context =
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Translations using IQueryable and I
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LINQ to DataSet335where defect.Fiel
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LINQ to DataSet337Creating and popu
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LINQ to XML339■ Create a document
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LINQ to XML341You can nest query ex
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LINQ to XML343need the string form,
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LINQ beyond .NET 3.5345Listing 12.1
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LINQ beyond .NET 3.5347LINQ TO ACTI
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LINQ beyond .NET 3.5349All of the L
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Summary351you look back at all the
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The changing nature of language pre
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Delegation as the new inheritance35
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Life in a parallel universe357Array
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appendix:LINQ standardquery operato
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Conversion361Cast and OfType conver
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Equality operations363A.4 Element o
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Joins365A.7 GroupingThere are two g
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Quantifiers367Table A.9Partitioning
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Sorting369For the examples of these
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indexSymbols!= 82with generics 76#p
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INDEX 373C# (continued)influences 1
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INDEX 375confusion 150, 222over cap
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INDEX 377Document Object Model (DOM
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INDEX 379fully qualified type name
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INDEX 381interfaces (continued)no c
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INDEX 383List`1 93lists 278local va
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INDEX 385Nullable (continued)Value
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INDEX 387RRails 22random access 102
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INDEX 389Standard Query Operators (
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INDEX 391type parameters (continued
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C# in Depth

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