FIELDS AND DATA CONSTANTS in VB.NET

Drawer PDF417 in VB.NET FIELDS AND DATA CONSTANTS

CHAPTER 9 FIELDS AND DATA CONSTANTS
PDF 417 Creation In VB.NET
Using Barcode encoder for .NET Control to generate, create PDF417 image in VS .NET applications.
www.OnBarcode.com
PDF-417 2d Barcode Decoder In Visual Basic .NET
Using Barcode recognizer for .NET framework Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
.field public static valuetype MultiDword multi_dword ... ldc.i1.1 ldsflda valuetype MultiDword multi_dword // Load reference to the field // As instance of MultiDword stfld uint8 MultiDword::b3 // Set value of third byte
Making Barcode In Visual Basic .NET
Using Barcode encoder for .NET framework Control to generate, create Barcode image in .NET applications.
www.OnBarcode.com
Painting EAN13 In VB.NET
Using Barcode printer for Visual Studio .NET Control to generate, create EAN13 image in VS .NET applications.
www.OnBarcode.com
Constructors vs. Data Constants
Make ANSI/AIM Code 39 In Visual Basic .NET
Using Barcode encoder for .NET Control to generate, create Code 39 Full ASCII image in Visual Studio .NET applications.
www.OnBarcode.com
Draw PDF417 In VB.NET
Using Barcode encoder for Visual Studio .NET Control to generate, create PDF-417 2d barcode image in .NET applications.
www.OnBarcode.com
You ve already taken a look at field mapping as a technique of field initialization, and I ve listed the drawbacks and limitations of this technique. Field mapping has this distinct unmanaged scent about it, but the compilers routinely use it for field initialization nevertheless. Is there a way to get the fields initialized without mapping them Yes, there is. The common language runtime object model provides two special methods, the instance constructor (.ctor) and the class constructor (.cctor), a.k.a. the type initializer. We re getting ahead of ourselves a bit here; 10 discusses methods in general and constructors in particular, so I won t concentrate on the details here. For now, all we need to know about .ctor and .cctor is that .ctor is executed when a new instance of a type is created, and .cctor is executed after the type is loaded and before any one of the type members is accessed. The class constructors are static and can deal with static members of the type only, so we have a perfect setup for field initialization: .cctors take care of static fields, and .ctors take care of instance fields. But how about global fields The good news is that we can define a global .cctor. Field initialization by constructors is vastly superior to field mapping, with none of its limitations, as described earlier in the section Mapped Fields. The catch Unfortunately, initialization by constructors must be executed at run time, burning processor cycles, whereas mapped fields simply are there after the module has been loaded. The mapped fields don t require additional operations for the initialization. Whether this price is worth the increased freedom and safety regarding field initialization depends on the concrete situation, but in general I think it is. Let me illustrate the point by building an alternative enumeration. Since all the values of an enumeration are stored in literal fields, which are inaccessible from IL directly, the compilers replace references to these fields with the respective values at compile time. We can use a very simple enum as a model: .class public enum sealed MagicNumber { .field private specialname int32 value__ .field public static literal valuetype MagicNumber MagicOne = int32(123) .field public static literal valuetype MagicNumber MagicTwo = int32(456) .field public static literal valuetype MagicNumber MagicThree = int32(789) }
DataMatrix Creation In Visual Basic .NET
Using Barcode printer for VS .NET Control to generate, create DataMatrix image in .NET framework applications.
www.OnBarcode.com
ANSI/AIM ITF 25 Generator In VB.NET
Using Barcode creation for VS .NET Control to generate, create 2 of 5 Interleaved image in VS .NET applications.
www.OnBarcode.com
CHAPTER 9 FIELDS AND DATA CONSTANTS
PDF-417 2d Barcode Scanner In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Printing PDF 417 In Java
Using Barcode creation for Java Control to generate, create PDF 417 image in Java applications.
www.OnBarcode.com
Let s suppose that our code uses the symbolic constants of an enumeration declared in a third-party assembly. We compile the code, and the symbolic constants are replaced with their values. Forget for a moment that we must have that third-party assembly available at compile time. But we will need to recompile the code every time the enumeration changes, and we have no control over the enumeration because it is defined outside our jurisdiction. In another scenario, when we declare an enumeration in one of our own modules, we must recompile all the modules that reference this enumeration once it is changed. Let s suppose also for the sake of an argument that we don t like this situation, so we decide to devise our own enumeration: .class public value sealed MagicNumber { .field public int32 _value_ // Specialname value__ is // reserved for enums .field public static valuetype MagicNumber MagicOne at D_00 .field public static valuetype MagicNumber MagicTwo at D_04 .field public static valuetype MagicNumber MagicThree at D_08 } .data D_00 = int32(123) .data D_04 = int32(456) .data D_08 = int32(789) This solution looks good, except in the platform-independence department. We conquered the recompilation problem and can at last address the symbolic constants by their symbols (names), through field access instructions. This approach presents a problem, though: the fields representing the symbolic constants can be written to. Let s try again with a class constructor; refer to the sample MyEnums.il on the Apress Web site: .class public value sealed MagicNumber { .field private int32 _value_ // Specialname value__ is // reserved for enums .field public static initonly valuetype MagicNumber MagicOne .field public static initonly valuetype MagicNumber MagicTwo .field public static initonly valuetype MagicNumber MagicThree .method public static specialname void .cctor() { ldsflda valuetype MagicNumber MagicNumber::MagicOne ldc.i4 123 stfld int32 MagicNumber::_value_ ldsflda valuetype MagicNumber MagicNumber::MagicTwo ldc.i4 456 stfld int32 MagicNumber::_value_ ldsflda valuetype MagicNumber MagicNumber::MagicThree ldc.i4 789 stfld int32 MagicNumber::_value_
Generating DataMatrix In Java
Using Barcode creator for Android Control to generate, create DataMatrix image in Android applications.
www.OnBarcode.com
Recognize Barcode In Visual C#
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in .NET applications.
www.OnBarcode.com
Print Barcode In Objective-C
Using Barcode creator for iPad Control to generate, create Barcode image in iPad applications.
www.OnBarcode.com
Painting Barcode In Visual C#
Using Barcode encoder for Visual Studio .NET Control to generate, create Barcode image in .NET framework applications.
www.OnBarcode.com
EAN-13 Supplement 5 Printer In None
Using Barcode maker for Word Control to generate, create EAN-13 Supplement 5 image in Office Word applications.
www.OnBarcode.com
Recognize GTIN - 12 In VB.NET
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Scan Data Matrix ECC200 In Visual C#
Using Barcode reader for VS .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Generate ECC200 In None
Using Barcode printer for Microsoft Excel Control to generate, create DataMatrix image in Excel applications.
www.OnBarcode.com
Code 128 Code Set B Decoder In .NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
UPCA Encoder In None
Using Barcode maker for Online Control to generate, create GS1 - 12 image in Online applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.