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Figure 8-7. Subquery composition In the later section “Interpreted Queries” on page 339, we’ll describe how remote sources such as SQL tables can be queried. Our example makes an ideal database query, because it would be processed as a unit, requiring only one round trip to the database server. This query, however, is inefficient for a local collection because the subquery is recalculated on each outer loop iteration. We can avoid this inefficiency by running the subquery separately (so that it’s no longer a subquery): int shortest = names.Min (n => n.Length); IEnumerable query = from n in names where n.Length == shortest select n; Factoring out subqueries in this manner is nearly always desirable when querying local collections. An exception is when the subquery is correlated, meaning that it references the outer range variable. We explore correlated subqueries in the following chapter, in the section “Projecting” on page 369. Subqueries and Deferred Execution An element or aggregation operator such as First or Count in a subquery doesn’t force the outer query into immediate execution—deferred execution still holds for the outer query. This is because subqueries are called indirectly—through a delegate in the case of a local query, or through an expression tree in the case of an interpreted query. An interesting case arises when you include a subquery within a Select expression. In the case of a local query, you’re actually projecting a sequence of queries—each 332 | Chapter 8: LINQ Queries
Figure 8-8. UML subquery composition itself subject to deferred execution. The effect is generally transparent, and it serves to further improve efficiency. We revisit Select subqueries in some detail in Chapter 9. Composition Strategies In this section, we describe three strategies for building more complex queries: • Progressive query construction • Using the into keyword • Wrapping queries All are chaining strategies and produce identical runtime queries. Composition Strategies | 333 LINQ Queries
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C# 4.0 www.free-ebooks-library.com
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C# 4.0 in a Nutshell, Fourth Editio
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Structs 89 Access Modifiers 90 Inte
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Annotations 440 Projecting into an
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Emitting Generic Methods and Types
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Groups 985 Replacing and Splitting
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If you’re already familiar with C
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This icon signifies a tip, suggesti
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I have the highest praise for Jon S
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Properties, methods, and events In
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Figure 1-1. This depicts the topics
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object o1 = "foo.doc"; object o2 =
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The first statement computes the ex
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The name of the C# compiler is csc.
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With contextual keywords, ambiguity
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Custom Type Examples Just as we can
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} } The public keyword The public k
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Figure 2-2. Assignment copies a val
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Technically, the CLR positions fiel
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Numeric literal type inference By d
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+ Addition − Subtraction * Multip
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In this case, x and y are implicitl
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which breaks equality and compariso
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Strings and Characters C#’s char
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Arrays An array represents a fixed
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int[,] matrix = new int[,] { {0,1,2
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Variables and Parameters A variable
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The following code outputs 0, becau
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static void Foo (ref int p) { p = p
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for (int i = 0; i < ints.Length; i+
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var—Implicitly Typed Local Variab
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Operator Precedence and Associativi
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Category Operator symbol Operator n
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Expression statements x = 1 + 2; //
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The switch statement switch stateme
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For example, the following prints t
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The return statement The return sta
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Rules Within a Namespace Name scopi
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namespace N2 { class Class3 : Class
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The :: token is used for namespace
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Fields allow the following modifier
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Overloading constructors A class or
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Object Initializers Versus Optional
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Properties allow the following modi
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Here’s how we could use this inde
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If a static constructor throws an u
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In addition, each participant can i
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Casting and Reference Conversions A
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public class Asset { public string
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Overrider over = new Overrider(); B
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Constructor and field initializatio
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Boxing and Unboxing Boxing is the a
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The ToString Method The ToString me
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Changing struct to class makes this
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Interfaces An interface is similar
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type that implements ISerializable
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public class RichTextBox : TextBox
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Center } A translation between the
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Unfortunately, Enum.IsDefined does
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Generic Types C# generics and C++ t
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static void Swap (ref T a, ref T b)
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Generic Constraints By default, a t
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Self-Referencing Generic Declaratio
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Classes Covariance and contravarian
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The IEnumerator and IEnumerable int
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The reason is that Max needs to be
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Technically, we are specifying a me
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Multicast delegate example Suppose
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The Func and Action Delegates With
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The following, however, is permitte
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Events When using delegates, two em
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public class PriceChangedEventArgs
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if (price == value) return; OnPrice
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Here is an example that illustrates
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Capturing Outer Variables A lambda
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Anonymous Methods Anonymous methods
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OUTPUT: x cannot be zero program co
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• The try block finishes normally
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The other common scenario is to ret
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indeterminate state that is the res
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class Enumerable // Typically imple
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Iterator Semantics An iterator is a
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yield return prevFib; int newFib =
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object o = "string"; int? x = o as
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Console.WriteLine (n | f); // (null
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== != > < >=
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Note n = (Note)554.37; // explicit
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Extension Method Chaining Extension
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static void Main() { string[] strin
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Now let’s change the static type
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Dynamic binding also incurs a perfo
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The static type of a variable decla
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The call to Foo(o,d) is dynamically
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parameters. The following attribute
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Value types declared inline within
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} } Pointers to Unmanaged Code Poin
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Compiler warnings can be extremely
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... Indicates a multiline code sam
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M:NS.MyClass.Z(System.Char[ ],Syste
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Table 5-1. C#, CLR, and .NET Framew
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Text Processing The System.Text nam
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this metadata at runtime, and do su
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infrastructure. Web Forms has been
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Provider layer The provider model d
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Remoting and Web Services Remoting
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ecause in Turkey, char.ToUpper ('i'
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string empty = ""; Console.WriteLin
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The static Join method does the rev
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order—but even then not exactly a
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The following performs a case-insen
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UTF-32 is the least space-efficient
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Two-word characters are called surr
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An excellent article on the rationa
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You can also construct a DateTime w
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The Add method adds a TimeSpan to a
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You can construct a DateTime that d
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source and destination TimeZoneInfo
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Western Australia is actually uniqu
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ToString and Parse The simplest for
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The next example formats a DateTime
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The following custom format provide
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Letter Meaning Sample input Result
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Figure 6-1. Composite NumberStyles
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The format strings "r", "R", and "u
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Other Conversion Mechanisms In the
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XmlConvert If you’re dealing with
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The .NET Framework helps you with t
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The Round method lets you specify t
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If you don’t want reproducibility
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static object GetBoxedIntegralValue
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Tuples Framework 4.0 provides a new
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Value Versus Referential Equality T
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Why the Complexity? You might wonde
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The IEquatable interface A conseque
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How to override equality semantics
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Implementing IEquatable For complet
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The .NET Framework also provides pl
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if (Equals (other)) return 0; // Fa
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Environment The static System.Envir
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7 Collections The .NET Framework pr
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By defining a single method retunin
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You can also subclass an existing c
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{ get { if (currentIndex == −1) t
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The ICollection and IList Interface
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IList and IList IList is the standa
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Because Array is a class, arrays ar
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void WriteFirstValue (Array a) { Co
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public static int FindIndex (T[] ar
Page 301 and 302: The Comparison delegate follows the
Page 303 and 304: List and ArrayList The generic List
Page 305 and 306: Such casts cannot be verified by th
Page 307 and 308: Here’s a demonstration on the use
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Page 311 and 312: public virtual SortedSet GetViewBet
Page 313 and 314: IDictionary IDictionary defines the
Page 315 and 316: Its underlying hashtable works by c
Page 317 and 318: var sorted = new SortedList (); for
Page 319 and 320: public class Animal { public string
Page 321 and 322: A keyed collection has some resembl
Page 323 and 324: clumsy hook methods like Collection
Page 325 and 326: Recall the requirements of a hashta
Page 327 and 328: IComparer and Comparer Comparers ar
Page 329 and 330: { public abstract int Compare (stri
Page 331 and 332: 8 LINQ Queries LINQ, or Language In
Page 333 and 334: We could further shorten our code b
Page 335 and 336: We already introduced the Where ope
Page 337 and 338: output sequence. In the case of the
Page 339 and 340: Natural Ordering The original order
Page 341 and 342: Figure 8-2. Query syntax The compil
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Page 345 and 346: Reevaluation Subqueries provide ano
Page 347 and 348: How Deferred Execution Works Query
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Page 351: The term subquery, in the general s
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Page 361 and 362: IQueryable query = from c in custom
Page 363 and 364: To work, LINQ to SQL needs some clu
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Page 367 and 368: LINQ to SQL Versus Entity Framework
Page 369 and 370: Unlike with L2S, however, a class s
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Page 381 and 382: Purpose LINQ to SQL Entity Framewor
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Page 385 and 386: Figure 8-12. Expression tree We can
Page 387 and 388: 9 LINQ Operators This chapter descr
Page 389 and 390: Overview In this section, we provid
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Thinking in query syntax As we just
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from c in dataContext.Customers fro
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Joining If you’re used to writing
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To see the benefit of Join over Sel
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GroupJoin GroupJoin does the same w
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You can create and query lookups ma
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OrderBy, OrderByDescending, ThenBy,
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var query = names.OrderBy (s => s.L
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from file in files group file.ToUpp
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In the next example, we filter the
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public static IEnumerable Cast (IE
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Method Description SQL equivalents
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Count simply enumerates over a sequ
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The first argument to Aggregate is
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Quantifiers IEnumerable→bool Meth
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10 LINQ to XML The .NET Framework p
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Figure 10-1. Core X-DOM types Figur
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XElement client = config.Element ("
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); new XElement ("lastname", c.Last
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Child Node Navigation Return type M
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The first call to Elements binds to
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Return type Members Defined in IEnu
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The ReplaceXXX methods are equivale
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Setting Values There are two ways t
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var e1 = new XElement ("test", "Hel
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Console.WriteLine (doc.Root.Parent
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XML file into another. Second, name
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Specifying Namespaces in the X-DOM
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foreach (XElement e in data.Descend
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A public type such as string doesn
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know about IQueryable, so it forces
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ObjectGraph.cs Program.cs Propertie
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11 Other XML Technologies The Syste
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Reading Nodes The units of an XML s
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Element----------> quote CDATA-----
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eader.ReadStartElement ("customerLi
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The XmlReader must be positioned on
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XmlWriter XmlWriter is a forward-on
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Patterns for Using XmlReader/XmlWri
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if (isEmpty) return; // element! w
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using (XmlWriter w = XmlWriter.Crea
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Setting the InnerText property repl
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XPath queries are expressed in term
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The [] operator filters a selection
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OUTPUT: Jim Thomas XSD and Schema V
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settings.ValidationEventHandler +=
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12 Disposal and Garbage Collection
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These rules are also helpful when w
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The idea is that a consumer of this
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public void Test() { byte[] myArray
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Figure 12-1. Roots deleted right aw
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objects with finalizers (because su
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public class TempFileRef { public r
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Figure 12-2. Heap generations The l
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dynamically tweaks the thresholds f
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Timers Forgotten timers can also ca
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var sb = new StringBuilder ("this i
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public TDelegate Target { get { var
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13 Diagnostics and Code Contracts W
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MyCompany.Widgets.Gadget; #endif Yo
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Both the Debug and Trace classes pr
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EventLog.CreateEventSource ("DemoAp
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if (list.Contains(item)) return fal
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The binary rewriter After compiling
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Preconditions should access only me
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• It’s time-consuming. • Call
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The binary rewriter moves postcondi
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For the reason just stated, postcon
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A special mechanism lets specify a
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Handling this event is particularly
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3. In the debug configuration of th
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Attaching and Breaking The static D
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If you instantiate a StackTrace obj
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2. Decide on a source name and crea
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The following sections illustrate h
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{ if (!PerformanceCounterCategory.E
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If you later want to define more co
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Figure 14-1. Stream architecture St
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In the following example, we use a
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Seeking A stream is seekable if Can
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OpenWrite and Create differ in beha
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[Flags] public enum FileAccess { Re
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Pipes are stream-based, so one proc
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Console.WriteLine (Encoding.UTF8.Ge
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Console.WriteLine (fs.Position); //
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is passed in (optionally through an
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using (TextWriter w = File.CreateTe
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public void SaveData (Stream s) { v
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The File Class File is a static cla
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using System.Runtime.InteropService
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FileInfo offers most of the File’
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Special Folders You must delete the
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watcher.Created += FileCreatedChang
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Memory-Mapped Files and Shared Memo
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using (TextWriter w = new StreamWri
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Isolation Types Isolated storage ca
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IsolatedStorageFile is poorly named
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s.WriteByte (100); f.DeleteFile (@"
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Figure 15-1. Network architecture I
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IPAddress a3 = IPAddress.Parse ("[3
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Uri u = new Uri ("page.html", UriKi
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2. Assign the Proxy property. 3. As
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If you don’t have a proxy, you mu
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Windows protocol that boils down to
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2. Examine the response object’s
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System.IO.File.WriteAllBytes ("Sear
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you greater privileges in browsing
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In this example, we sleep for 500 m
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without needing more threads—by f
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Using DNS In all these examples, yo
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Using TCP TCP and UDP constitute th
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Hello Hello right back! In this exa
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In this example, we write each mail
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Serialization Engines There are fou
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an arbitrary XML structure. For ins
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It requires, however, that you expl
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Specifying a name and namespace dec
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The solution is to specify all perm
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we would see the same address detai
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Null and Empty Values There are two
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Subclassed Collection Elements The
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[DataMember (Name="Addresses")] Ser
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The following example illustrates a
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The two formatters are otherwise ex
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[OnSerializing] and [OnSerialized]
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Binary Serialization with ISerializ
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Subclassing Serializable Classes In
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XmlSerializer xs = new XmlSerialize
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and you write a reusable method to
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If, on the other hand, you want the
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instead add [XmlElement] to the col
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public void WriteXml (XmlWriter wri
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Assemblies are structured similarly
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To embed an application manifest fi
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Table 17-1. Assembly members Functi
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Delay Signing In an organization wi
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If the assembly has no AssemblyVers
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Figure 17-3. Unsigned file warning
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Signing with signtool.exe You can A
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• Updating assemblies in the GAC
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.mresource public banner.jpg { // O
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GetManifestResourceNames returns th
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(The first argument must be namespa
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We then retrieved the greeting at r
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where to look. You (or Visual Studi
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Loading from a filename You can see
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if (!File.Exists (path)) return nul
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for the presence of a library in it
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18 Reflection and Metadata As we sa
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Obtaining array types As we just sa
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Base Types and Interfaces Type expo
Page 707 and 708:
Console.WriteLine (staticD.DynamicI
Page 709 and 710:
When calling GetMembers, you can pa
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C# construct Method to use Name to
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Console.WriteLine (unbound.Property
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from m in typeof (Enumerable).GetMe
Page 717 and 718:
The following example retrieves all
Page 719 and 720:
There’s no nongeneric type we can
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Modules Calling GetTypes on a multi
Page 723 and 724:
The AttributeUsage Attribute Attrib
Page 725 and 726:
Retrieving Attributes at Runtime Th
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AppDomain.CurrentDomain.ReflectionO
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gen.Emit (OpCodes.Ldc_I4, 123); //
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gen.Emit (OpCodes.Mul); // Multiply
Page 733 and 734:
Type[] strT = { typeof (string) };
Page 735 and 736:
The DefineType method also accepts
Page 737 and 738:
We could just as easily call a dyna
Page 739 and 740:
mb.DefineParameter (1, ParameterAtt
Page 741 and 742:
ILGenerator setGen = setter.GetILGe
Page 743 and 744:
myFieldBuilder.SetCustomAttribute (
Page 745 and 746:
Awkward Emission Targets All the ex
Page 747 and 748:
and object references. In creating
Page 749 and 750:
Here is a sample of the output our
Page 751 and 752:
The next step is to call FormatOper
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The point where we call ResolveMemb
Page 756 and 757:
trees (the same expression trees in
Page 758 and 759:
yte b = 3; Console.WriteLine ((b +
Page 760 and 761:
DynamicVisit on each person in the
Page 762 and 763:
Anonymously Calling Members of a Ge
Page 764 and 765:
Notice that we used dynamic member
Page 766 and 767:
The following does a similar thing
Page 768 and 769:
In the following example, we use Ir
Page 771 and 772:
In this chapter, we discuss the two
Page 773 and 774:
Framework 4.0 deprecates support fo
Page 775 and 776:
When you call AddPermission, the pe
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if you access the chosen file by ca
Page 779 and 780:
Elevation of Privilege Let’s supp
Page 781 and 782:
The Transparency Model in CLR 4.0 T
Page 783 and 784:
Figure 20-1. Transparency model; on
Page 785 and 786:
GC.AddMemoryPressure (1000000); //
Page 787 and 788:
stack, the WindowFromPoint method w
Page 789 and 790:
string dir = Path.Combine (System.R
Page 791 and 792:
The first step in doing this is to
Page 793 and 794:
A feature called User Access Contro
Page 795 and 796:
If you replace requireAdministrator
Page 797 and 798:
Table 20-8. Encryption and hashing
Page 799 and 800:
The GetBytes method on an Encoding
Page 801 and 802:
As well as a key, we made up an IV,
Page 803 and 804:
w.WriteLine ("Small and secure!");
Page 805 and 806:
pairs. A key pair contains a public
Page 807 and 808:
using (var rsaPublicPrivate = new R
Page 809 and 810:
C# allows you to execute code in pa
Page 811 and 812:
Getting Started A client program (C
Page 813 and 814:
Thread.Sleep(0) relinquishes the th
Page 815 and 816:
string text = "t1"; Thread t1 = new
Page 817 and 818:
If this program is called with no a
Page 819 and 820:
The try/catch statement in this exa
Page 821 and 822:
There are a few things to be wary o
Page 823 and 824:
static void Main() { ThreadPool.Que
Page 825 and 826:
we’re using it to pass the method
Page 827 and 828:
Fortunately, the pool manager has a
Page 829 and 830:
class ThreadUnsafe { static int _va
Page 831 and 832:
As with the Enter method, it’s ov
Page 833 and 834:
Instruction atomicity is a differen
Page 835 and 836:
BeginInvoke instead of Invoke. Alte
Page 837 and 838:
static void Main() { for (int i = 1
Page 839 and 840:
class ThreadSafe { static List _li
Page 841 and 842:
In the absence of documentation, it
Page 843 and 844:
The code is similar for Windows For
Page 845 and 846:
It’s also possible to safely assi
Page 847 and 848:
The following implicitly generate f
Page 849 and 850:
As it happens, Intel’s X86 and X6
Page 851 and 852:
Exchange and CompareExchange method
Page 853 and 854:
former two are based on the common
Page 855 and 856:
Two-way signaling Let’s say we wa
Page 857 and 858:
Signaling Constructs and Performanc
Page 859 and 860:
Signaling worker... Started - Some
Page 861 and 862:
and the lock statement, you can ach
Page 863 and 864:
This means that despite appearances
Page 865 and 866:
using System; using System.Threadin
Page 867 and 868:
We don’t pulse after dequeuing, a
Page 869 and 870:
Use of PulseAll would forgo fairnes
Page 871 and 872:
The Event-Based Asynchronous Patter
Page 873 and 874:
class Program { static BackgroundWo
Page 875 and 876:
Reached 20% Reached 40% Reached 60%
Page 877 and 878:
For a discussion as to why aborting
Page 879 and 880:
Cancellation Tokens Framework 4.0 p
Page 881 and 882:
if (_expensive == null) _expensive
Page 883 and 884:
you want to keep data isolated, ens
Page 885 and 886:
from under their feet, as long as t
Page 887 and 888:
Here’s the result: Thread B added
Page 889 and 890:
var rw = new ReaderWriterLockSlim()
Page 891 and 892:
class SystemTimer { static void Mai
Page 893 and 894:
22 Parallel Programming In this cha
Page 895 and 896:
Data parallelism is also conducive
Page 897 and 898:
the code that must execute sequenti
Page 899 and 900:
Why Isn’t AsParallel the Default?
Page 901 and 902:
Most query operators change the ind
Page 903 and 904:
.Select (i => wordList [localRandom
Page 905 and 906:
class Camera { public readonly int
Page 907 and 908:
foreach (int n in parallelQuery) Do
Page 909 and 910:
Figure 22-4. Chunk versus range par
Page 911 and 912:
string text = "Let's suppose this i
Page 913 and 914:
public static void Invoke (Parallel
Page 915 and 916:
var random = new Random(); string[]
Page 917 and 918:
public static ParallelLoopResult Fo
Page 919 and 920:
• Wait on a set of tasks—withou
Page 921 and 922:
The task queuing problem arises bec
Page 923 and 924:
TaskCreationOptions atp = TaskCreat
Page 925 and 926:
As soon as task1 (the antecedent) f
Page 927 and 928:
Conditional continuations By defaul
Page 929 and 930:
This writes “Done” after writin
Page 931 and 932:
var factory = new TaskFactory ( Tas
Page 933 and 934:
Flatten and Handle Both PLINQ and t
Page 935 and 936:
• The concurrent stack, queue, an
Page 937 and 938:
Concurrent bags are ideal when the
Page 939 and 940:
public class PCQueue : IDisposable
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If you leave a spinlock contended f
Page 943 and 944:
How to use SpinWait There are two w
Page 945:
spinWait.SpinOnce(); } } Here’s h
Page 948 and 949:
If you don’t need such concurrenc
Page 950 and 951:
• The underlying implementation
Page 952 and 953:
public class Server { public void S
Page 954 and 955:
void Read() { _stream.BeginRead (_d
Page 956 and 957:
_stream = c.GetStream(); var task =
Page 958 and 959:
exception is encountered, it’s no
Page 960 and 961:
When writing asynchronous methods,
Page 963 and 964:
24 Application Domains An applicati
Page 965 and 966:
Creating and Destroying Application
Page 967 and 968:
When additional application domains
Page 969 and 970:
static void Main() { AppDomain newD
Page 971 and 972:
class Client { // Here's a static f
Page 973 and 974:
it appears as though it was a direc
Page 975 and 976:
namespace Plugin.Extensions { publi
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25 Native and COM Interoperability
Page 979 and 980:
class Test { [DllImport("kernel32.d
Page 981 and 982:
StringBuilder class require copying
Page 983 and 984:
Shared Memory Memory-mapped files,
Page 985 and 986:
The second application subscribes t
Page 987 and 988:
If you’re targeting Framework 4.0
Page 989 and 990:
With the first use of the fixed key
Page 991 and 992:
The root interface in COM is IUnkno
Page 993 and 994:
workBook.SaveAs (@"c:\test.xlsx", P
Page 995 and 996:
Embedding Interop Types We said pre
Page 997 and 998:
26 Regular Expressions The regular
Page 999 and 1000:
Regex r = new Regex (@"sausages?");
Page 1001 and 1002:
Character Sets Character sets act a
Page 1003 and 1004:
The problem is that our * quantifie
Page 1005 and 1006:
The positive lookahead ensures that
Page 1007 and 1008:
The following example matches a sim
Page 1009 and 1010:
Extracting "name = value" pairs (on
Page 1011 and 1012:
Console.WriteLine (m.Groups ["tag"]
Page 1013 and 1014:
Expression Meaning Inverse (“not
Page 1015:
Table 26-11. Miscellaneous construc
Page 1018 and 1019:
catch A keyword for the clause in a
Page 1020 and 1021:
goto A jump statement that jumps to
Page 1022 and 1023:
ef A parameter and argument modifie
Page 1024 and 1025:
volatile A field modifier instructi
Page 1026 and 1027:
A with enums, 98 with nullable type
Page 1028 and 1029:
inary numbers (converting), 233 bin
Page 1030 and 1031:
COM type system, 970 IUnknown and I
Page 1032 and 1033:
time zones, 213-218 TimeSpan, 206 D
Page 1034 and 1035:
Array class, 277 enumerators, 143 I
Page 1036 and 1037:
formatting, 219-225 composite forma
Page 1038 and 1039:
IndexOf method, 196, 279 IndexOfAny
Page 1040 and 1041:
Count and LongCount, 407 Min and Ma
Page 1042 and 1043:
memory barriers and volatility, 825
Page 1044 and 1045:
PipeStream class, 547 anonymous pip
Page 1046 and 1047:
Remoting, 952 remove keyword, 124 R
Page 1048 and 1049:
two-word characters and, 206 String
Page 1050 and 1051:
DateTime and, 213 DateTimeOffset an
Page 1052 and 1053:
loading and parsing, 416 names and
Page 1055:
About the Authors Joe Albahari is t
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