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Preconditions (Level 2) Enables all preconditions (Level 1 plus normal preconditions) Pre and Post (Level 3) Enables Level2 checking plus postconditions Full (Level 4) Enables Level 3 checking plus object invariants and assertions (i.e., everything) You typically enable full contract checking in debug build configurations. Contracts in Release Builds When it comes to making release builds, there are two general philosophies: • Favor safety and enable full contract checking • Favor performance and disable all contract checking If you’re building a library for public consumption, though, the second approach creates a problem. Imagine that you compile and distribute library L in release mode with contract checking disabled. A client then builds project C in debug mode that references library L. Assembly C can then call members of L incorrectly without contract violations! In this situation, you actually want to enforce the parts of L’s contract that ensure correct usage of L—in other words, the preconditions in L’s public members. The simplest way to resolve this is to enable /publicsurface checking in L with a level of Preconditions or ReleaseRequires. This ensures that the essential preconditions are enforced for the benefit of consumers, while incurring the performance cost of only those preconditions. In extreme cases, you might not want to pay even this small performance price—in which case, you can take the more elaborate approach of call-site checking. Call-Site Checking Call-site checking moves precondition validation from called methods into calling methods (call sites). This solves the problem just described—by enabling consumers of library L to perform L’s precondition validation themselves in debug configurations. To enable call-site checking, you must first build a separate contracts reference assembly—a supplementary assembly that contains just the preconditions for the referenced assembly. To do this, you can either use the ccrefgen command-line tool, or proceed in Visual Studio as follows: 1. In the release configuration of the referenced library (L), go to the Code Contracts tab of Project Properties and disable runtime contract checking while ticking “Build a Contract Reference Assembly”. This then generates a supplementary contracts reference assembly (with the suffix .contracts.dll). 2. In the release configuration of the referencing assemblies, disable all contract checking. 522 | Chapter 13: Diagnostics and Code Contracts
3. In the debug configuration of the referencing assemblies, tick “Call-site Requires Checking.” The third step is equivalent to calling ccrewrite with the /callsiterequires switch. It reads the preconditions from the contracts reference assembly and weaves them into the calling sites in the referencing assembly. Static Contract Checking Code contracts permit static contract checking, whereby a tool analyzes contract conditions to find potential bugs in your program before it’s run. For example, statically checking the following code generates a warning: static void Main() { string message = null; WriteLine (message); // Static checking tool will generate warning } static void WriteLine (string s) { Contract.Requires (s != null); Console.WriteLine (s); } You can run Microsoft’s static contracts tool either from the command line via cccheck, or by enabling static contract checking in Visual Studio’s project properties dialog (the commercial version is supported with Visual Studio Premium and Ultimate editions only). For static checking to work, you may need to add preconditions and postconditions to your methods. To give a simple example, the following will generate a warning: static void WriteLine (string s, bool b) { if (b) WriteLine (s); // Warning: requires unproven } static void WriteLine (string s) { Contract.Requires (s != null); Console.WriteLine (s); } Because we’re calling a method that requires the parameter to be non-null, we must prove that the argument is non-null. To do this, we can add a precondition to the first method as follows: static void WriteLine (string s, bool b) { Contract.Requires (s != null); if (b) WriteLine (s); // OK } Static Contract Checking | 523 Diagnostics and Code Contracts
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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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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
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The Comparison delegate follows the
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List and ArrayList The generic List
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public sealed class BitArray : ICol
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public virtual SortedSet GetViewBet
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IDictionary IDictionary defines the
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var sorted = new SortedList (); for
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public class Animal { public string
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clumsy hook methods like Collection
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Recall the requirements of a hashta
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IComparer and Comparer Comparers ar
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{ public abstract int Compare (stri
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8 LINQ Queries LINQ, or Language In
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We could further shorten our code b
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We already introduced the Where ope
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output sequence. In the case of the
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Natural Ordering The original order
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Figure 8-2. Query syntax The compil
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With LINQ, data logically flows fro
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Reevaluation Subqueries provide ano
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How Deferred Execution Works Query
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Adding ToList onto the end of this
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The term subquery, in the general s
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Figure 8-8. UML subquery compositio
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select n.Replace ("a", "").Replace
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(The compiler does not emit the fin
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where vowelless.Length > 2 orderby
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IQueryable query = from c in custom
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To work, LINQ to SQL needs some clu
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Figure 8-10. Combining local and in
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LINQ to SQL Versus Entity Framework
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Unlike with L2S, however, a class s
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The Single operator is ideal for re
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You can disable this behavior in L2
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With EF: [EdmRelationshipNavigation
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• It lets you request that certai
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context.SubmitChanges(); // Updates
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Purpose LINQ to SQL Entity Framewor
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void Test() { var dataContext = new
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Figure 8-12. Expression tree We can
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9 LINQ Operators This chapter descr
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Overview In this section, we provid
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Picks a single element from a seque
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In query syntax: IEnumerable query
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TakeWhile enumerates the input sequ
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IEnumerable query = names .Select (
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This is slightly untidy, however, i
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element is the trigger for the intr
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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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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
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Console.WriteLine (staticD.DynamicI
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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
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The following example retrieves all
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There’s no nongeneric type we can
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Modules Calling GetTypes on a multi
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The AttributeUsage Attribute Attrib
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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
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Type[] strT = { typeof (string) };
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The DefineType method also accepts
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We could just as easily call a dyna
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mb.DefineParameter (1, ParameterAtt
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ILGenerator setGen = setter.GetILGe
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myFieldBuilder.SetCustomAttribute (
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Awkward Emission Targets All the ex
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and object references. In creating
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Here is a sample of the output our
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The next step is to call FormatOper
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The point where we call ResolveMemb
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trees (the same expression trees in
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yte b = 3; Console.WriteLine ((b +
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DynamicVisit on each person in the
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Anonymously Calling Members of a Ge
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Notice that we used dynamic member
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The following does a similar thing
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In the following example, we use Ir
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In this chapter, we discuss the two
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Framework 4.0 deprecates support fo
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When you call AddPermission, the pe
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if you access the chosen file by ca
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Elevation of Privilege Let’s supp
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The Transparency Model in CLR 4.0 T
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Figure 20-1. Transparency model; on
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GC.AddMemoryPressure (1000000); //
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stack, the WindowFromPoint method w
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string dir = Path.Combine (System.R
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The first step in doing this is to
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A feature called User Access Contro
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If you replace requireAdministrator
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Table 20-8. Encryption and hashing
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The GetBytes method on an Encoding
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As well as a key, we made up an IV,
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w.WriteLine ("Small and secure!");
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pairs. A key pair contains a public
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using (var rsaPublicPrivate = new R
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C# allows you to execute code in pa
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Getting Started A client program (C
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Thread.Sleep(0) relinquishes the th
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string text = "t1"; Thread t1 = new
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If this program is called with no a
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The try/catch statement in this exa
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There are a few things to be wary o
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static void Main() { ThreadPool.Que
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we’re using it to pass the method
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Fortunately, the pool manager has a
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class ThreadUnsafe { static int _va
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As with the Enter method, it’s ov
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Instruction atomicity is a differen
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BeginInvoke instead of Invoke. Alte
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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
Page 941 and 942:
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
Page 977 and 978:
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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