C# in Depth

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Parameterizedtyping with genericsThis chapter covers■Generic types and methods■ Generic collections in .NET 2.0■■Limitations of genericsComparisons with other languagesTrue 1 story: the other day my wife and I did our weekly grocery shopping. Justbefore we left, she asked me if I had the list. I confirmed that indeed I did have thelist, and off we went. It was only when we got to the grocery store that our mistakemade itself obvious. My wife had been asking about the shopping list whereas I’dactually brought the list of neat features in C# 2. When we asked an assistantwhether we could buy any anonymous methods, we received a very strange look.If only we could have expressed ourselves more clearly! If only she’d had someway of saying that she wanted me to bring the list of items we wanted to buy! If onlywe’d had generics…1By which I mean “convenient for the purposes of introducing the chapter”—not, you know, accurate as such.63Licensed to Rhona Hadida
64 CHAPTER 3 Parameterized typing with genericsFor most people, generics will be the most important new feature of C# 2. Theyenhance performance, make your code more expressive, and move a lot of safetyfrom execution time to compile time. Essentially they allow you to parameterize typesand methods—just as normal method calls often have parameters to tell them whatvalues to use, generic types and methods have type parameters to tell them what typesto use. It all sounds very confusing to start with—and if you’re completely new togenerics you can expect a certain amount of head scratching—but once you’ve gotthe basic idea, you’ll come to love them.In this chapter we’ll be looking at how to use generic types and methods that othershave provided (whether in the framework or as third-party libraries), and how to writeyour own. We’ll see the most important generic types within the framework, and take alook just under the surface to understand some of the performance implications ofgenerics. To conclude the chapter, I’ll present some of the most frequently encounteredlimitations of generics, along with possible workarounds, and compare genericsin C# with similar features in other languages.First, though, we need to understand the problems that caused generics to bedevised in the first place.3.1 Why generics are necessaryHave you ever counted how many casts you have in your C# 1 code? If you use any ofthe built-in collections, or if you’ve written your own types that are designed to workwith many different types of data, you’ve probably got plenty of casts lurking in yoursource, quietly telling the compiler not to worry, that everything’s fine, just treat theexpression over there as if it had this particular type. Using almost any API that hasobject as either a parameter type or a return type will probably involve casts at somepoint. Having a single-class hierarchy with object as the root makes things morestraightforward, but the object type in itself is extremely dull, and in order to do anythinggenuinely useful with an object you almost always need to cast it.Casts are bad, m’kay? Not bad in an “almost never do this” kind of way (like mutablestructs and nonprivate fields) but bad in a “necessary evil” kind of way. They’re anindication that you ought to give the compiler more information somehow, and thatthe way you’re choosing is to get the compiler to trust you at compile time and generatea check to run at execution time, to keep you honest.Now, if you need to tell the compiler the information somewhere, chances are thatanyone reading your code is also going to need that same information. They can see itwhere you’re casting, of course, but that’s not terribly useful. The ideal place to keepsuch information is usually at the point of declaring a variable or method. This is evenmore important if you’re providing a type or method which other people will call withoutaccess to your code. Generics allow library providers to prevent their users from compilingcode that calls the library with bad arguments. Previously we’ve had to rely on manuallywritten documentation—which is often incomplete or inaccurate, and is rarely read anyway.Armed with the extra information, everyone can work more productively: the compileris able to do more checking; the IDE is able to present IntelliSense options basedLicensed 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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Page 63 and 64: Core foundations:building on C# 1Th
Page 65 and 66: 34 CHAPTER 2 Core foundations: buil
Page 86 and 87: C# 2 and 3: new features on a solid
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Page 90 and 91: Summary59Listing 2.7 shows a number
Page 92 and 93: Part 2C#2:solving the issuesof C#1I
Page 96 and 97: Simple generics for everyday use65o
Page 98 and 99: Simple generics for everyday use67I
Page 100 and 101: Simple generics for everyday use69t
Page 102 and 103: Simple generics for everyday use71N
Page 104 and 105: Simple generics for everyday use73}
Page 106 and 107: Beyond the basics75parameters. You
Page 108 and 109: Beyond the basics77NOTEC# vs. CLI s
Page 110 and 111: Beyond the basics79combined togethe
Page 112 and 113: Beyond the basics813.3.3 Implementi
Page 114 and 115: Beyond the basics83derive from a pa
Page 116 and 117: Advanced generics85implement IEquat
Page 118 and 119: Advanced generics87within another,
Page 120 and 121: Advanced generics89ArrayListobject[
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
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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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Novel uses of nullable types131part
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Novel uses of nullable types133else
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Novel uses of nullable types135}{}i
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Fast-tracked delegatesThis chapter
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Saying goodbye to awkward delegate
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Covariance and contravariance141met
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Covariance and contravariance143som
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Inline delegate actions with anonym
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Capturing variables in anonymous me
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Implementingiterators the easy wayT
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C# 1: the pain of handwritten itera
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C# 2: simple iterators with yield s
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Real-life example: iterating over r
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Pseudo-synchronous code with the Co
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Summary181(without using a dedicate
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Concluding C# 2:the final featuresT
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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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