C# in Depth

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Summary181(without using a dedicated thread) until it had completed, calling the supplied delegateto handle the result. It would then call MoveNext again, and our method wouldcontinue. This time we kick off two requests in parallel, and the CCR to call another delegatewith the results of both operations when they’ve both finished. After that, Move-Next is called for a final time and we get to complete the request processing.Although it’s obviously more complicated than the synchronous version, it’s still allin one method, it will get executed in the order written, and the method itself canhold the state (in the local variables, which become state in the extra type generatedby the compiler). It’s fully asynchronous, using as few threads as it can get away with. Ihaven’t shown any error handling, but that’s also available in a sensible fashion thatforces you to think about the issue at appropriate places.It all takes a while to get your head around (at least unless you’ve seen continuationpassingstyle code before) but the potential benefits in terms of writing correct, scalablecode are enormous—and it’s only feasible in such a neat way due to C# 2’s syntacticsugar around iterators and anonymous methods. The CCR hasn’t hit the mainstream atthe time of writing, but it’s possible that it will become another normal part of thedevelopment toolkit 11 —and that other novel uses for iterator blocks will be thought upover time. As I said earlier, the point of the section is to open your mind to possible usesof the work that the compiler can do for you beyond just simple iteration.6.5 SummaryC# supports many patterns indirectly, in terms of it being feasible to implement themin C#. However, relatively few patterns are directly supported in terms of language featuresbeing specifically targeted at a particular pattern. In C# 1, the iterator patternwas directly supported from the point of view of the calling code, but not from theperspective of the collection being iterated over. Writing a correct implementation ofIEnumerable was time-consuming and error-prone, without being interesting. In C# 2the compiler does all the mundane work for you, building a state machine to copewith the “call-back” nature of iterators.It should be noted that iterator blocks have one aspect in common with the anonymousmethods we saw in chapter 5, even though the actual features are very different.In both cases, extra types may be generated, and a potentially complicated code transformationis applied to the original source. Compare this with C# 1 where most of thetransformations for syntactic sugar (lock, using, and foreach being the most obviousexamples) were quite straightforward. We’ll see this trend toward smarter compilationcontinuing with almost every aspect of C# 3.As well as seeing a real-life example of the use of iterators, we’ve taken a look athow one particular library has used them in a fairly radical way that has little to dowith what comes to mind when we think about iteration over a collection. It’s worthbearing in mind that different languages have also looked at this sort of problem11 Some aspects of the CCR may also become available as part of the Parallel Extensions library described inchapter 13.Licensed to Rhona Hadida
182 CHAPTER 6 Implementing iterators the easy waybefore—in computer science the term coroutine is applied to concepts of this nature.Different languages have historically supported them to a greater or lesser extent,with tricks being applicable to simulate them sometimes—for example, SimonTatham has an excellent article 12 on how even C can express coroutines if you’re willingto bend coding standards somewhat. We’ve seen that C# 2 makes coroutines easyto write and use.Having seen some major and sometimes mind-warping language changes focusedaround a few key features, our next chapter is a change of pace. It describes a numberof small changes that make C# 2 more pleasant to work with than its predecessor,learning from the little niggles of the past to produce a language that has fewer roughedges, more scope for dealing with awkward backward-compatibility cases, and a betterstory around working with generated code. Each feature is relatively straightforward,but there are quite a few of them…12 http://www.chiark.greenend.org.uk/~sgtatham/coroutines.htmlLicensed 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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Advanced generics87within another,
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Advanced generics89ArrayListobject[
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Advanced generics91}{}return new Co
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Advanced generics93Listing 3.10Usin
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Advanced generics95REFLECTING GENER
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Generic collection classes in .NET
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Limitations of generics in C# and o
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Summary111My personal opinion is th
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What do you do when you just don’
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System.Nullable and System.Nullable
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C# 2’s syntactic sugar for nullab
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Page 162 and 163: Novel uses of nullable types131part
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Page 166 and 167: Novel uses of nullable types135}{}i
Page 168 and 169: Fast-tracked delegatesThis chapter
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 214 and 215: Concluding C# 2:the final featuresT
Page 216 and 217: Partial types185C# 2 allows more th
Page 218 and 219: Partial types187code generator can
Page 220 and 221: Partial types189Listing 7.2A partia
Page 222 and 223: Static classes191}public static str
Page 224 and 225: Namespace aliases193same syntax is
Page 226 and 227: Namespace aliases195Listing 7.6usin
Page 228 and 229: Pragma directives197}}Console.Write
Page 230 and 231: Fixed-size buffers in unsafe code19
Page 232 and 233: Exposing internal members to select
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Page 236 and 237: Part 3C# 3—revolutionizinghow we
Page 238 and 239: Cutting fluffwith a smart compilerT
Page 240 and 241: Automatically implemented propertie
Page 242 and 243: Implicit typing of local variables2
Page 244 and 245: Implicit typing of local variables2
Page 246 and 247: Simplified initialization215simple
Page 248 and 249: Simplified initialization217The par
Page 250 and 251: Simplified initialization219CREATIN
Page 252 and 253: Simplified initialization221Home =
Page 254 and 255: Implicitly typed arrays2238.4 Impli
Page 256 and 257: Anonymous types225new { Name = "Hol
Page 258 and 259: Anonymous types227That certainly wo
Page 260 and 261: 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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