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Attributes for Interoperation
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17.5Attributes for InteroperationNote: This section is applicable only to the Microsoft .NET implementation of C#. 17.5.1Interoperation with COM and Win32 componentsThe .NET runtime provides a large number of attributes that enable C# programs to interoperate with components written using COM and Win32 DLLs. For example, the DllImport attribute can be used on a static extern method to indicate that the implementation of the method is to be found in a Win32 DLL. These attributes are found in the System.Runtime.InteropServices namespace, and detailed documentation for these attributes is found in the .NET runtime documentation. 17.5.2Interoperation with other .NET languages17.5.2.1The IndexerName attributeIndexers are implemented in .NET using indexed properties, and have a name in the .NET metadata. If no IndexerName attribute is present for an indexer, then the name Item is used by default. The IndexerName attribute enables a developer to override this default and specify a different name. namespace System.Runtime.CompilerServices.CSharp { [AttributeUsage(AttributeTargets.Property)] public class IndexerNameAttribute: Attribute { public IndexerNameAttribute(string indexerName) {...} public string Value { get {...} } } } 18.Unsafe codeThe core C# language, as defined in the preceding chapters, differs notably from C and C++ in its omission of pointers as a data type. Instead, C# provides references and the ability to create objects that are managed by a garbage collector. This design, coupled with other features, makes C# a much safer language than C or C++. In the core C# language it is simply not possible to have an uninitialized variable, a “dangling” pointer, or an expression that indexes an array beyond its bounds. Whole categories of bugs that routinely plague C and C++ programs are thus eliminated. While practically every pointer type construct in C or C++ has a reference type counterpart in C#, nonetheless, there are situations where access to pointer types becomes a necessity. For example, interfacing with the underlying operating system, accessing a memory-mapped device, or implementing a time-critical algorithm may not be possible or practical without access to pointers. To address this need, C# provides the ability to write unsafe code. In unsafe code it is possible to declare and operate on pointers, to perform conversions between pointers and integral types, to take the address of variables, and so forth. In a sense, writing unsafe code is much like writing C code within a C# program. Unsafe code is in fact a “safe” feature from the perspective of both developers and users. Unsafe code must be clearly marked with the modifier unsafe, so developers can’t possibly use unsafe features accidentally, and the execution engine works to ensure that unsafe code cannot be executed in an untrusted environment. 18.1Unsafe contextsThe unsafe features of C# are available only in unsafe contexts. An unsafe context is introduced by including an unsafe modifier in the declaration of a type or member, or by employing an unsafe-statement:
The associated grammar extensions are shown below. For brevity, ellipses (...) are used to represent productions that appear in preceding chapters. class-modifier: ... unsafe struct-modifier: ... unsafe interface-modifier: ... unsafe delegate-modifier: ... unsafe field-modifier: ... unsafe method-modifier: ... unsafe property-modifier: ... unsafe event-modifier: ... unsafe indexer-modifier: ... unsafe operator-modifier: ... unsafe constructor-modifier: ... unsafe destructor-declaration: attributesopt externopt unsafeopt ~ identifier ( ) destructor-body attributesopt unsafeopt externopt ~ identifier ( ) destructor-body static-constructor-modifiers: externopt unsafeopt static unsafeopt externopt static externopt static unsafeopt unsafeopt static externopt static externopt unsafeopt static unsafeopt externopt embedded-statement: ... unsafe-statement unsafe-statement: unsafe block In the example public unsafe struct Node
the unsafe modifier specified in the struct declaration causes the entire textual extent of the struct declaration to become an unsafe context. Thus, it is possible to declare the Left and Right fields to be of a pointer type. The example above could also be written public struct Node
Here, the unsafe modifiers in the field declarations cause those declarations to be considered unsafe contexts. Other than establishing an unsafe context, thus permitting the use of pointer types, the unsafe modifier has no effect on a type or a member. In the example public class A { public unsafe virtual void F() { char* p; ... } } public class B: A { public override void F() { base.F(); ... } } the unsafe modifier on the F method in A simply causes the textual extent of F to become an unsafe context in which the unsafe features of the language can be used. In the override of F in B, there is no need to re-specify the unsafe modifier—unless, of course, the F method in B itself needs access to unsafe features. The situation is slightly different when a pointer type is part of the method’s signature public unsafe class A { public virtual void F(char* p) {...} } public class B: A { public unsafe override void F(char* p) {...} } Here, because F’s signature includes a pointer type, it can only be written in an unsafe context. However, the unsafe context can be introduced by either making the entire class unsafe, as is the case in A, or by including an unsafe modifier in the method declaration, as is the case in B. Directory: download download -> Performance Tuning Guidelines for Windows Server 2008 May 20, 2009 Abstract download -> Northern England’s set-jetting locations download -> Bbc archives: Beyond the programme download download -> Occupational health and safety download -> Dynatest 3031 lwd light Weight Deflectometer download -> Forth coming competitive exams download -> English Olympiad Tasks: 10 th form Аудіювання, 10 клас. Текст download -> Brush High School Morning Announcements Friday, September 05, 2014 all school download -> Year 9 The Arts — Music download -> Years 7 and 8 standard elaborations — Australian Curriculum: Music draft Download 3.2 Mb. Share with your friends:
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