NAMESPACES AND CLASSES in Visual Basic .NET

Printer PDF-417 2d barcode in Visual Basic .NET NAMESPACES AND CLASSES

Although this is not what you intended, it has no dire consequences just a case of mild confusion. If you know and expect this effect and don t get confused that easily, you can even forgo the namespace declarations altogether and declare classes by their full names, to match the way they are referenced: .class public 'X.Y.Z'{ ... } That s exactly how it is done in ILAsm v2.0, only without single quotes around the full class name, because ILAsm v2.0 allows dotted names as class or method names. The reason for switching from the namespace/name model of class declaration to the full-name model in ILAsm v2.0 is twofold. First, this way, the classes are declared and referenced uniformly by their full names. Second, this resolves the problem of naming the nested classes: if namespace A contains declaration of class B, which contains declaration of nested class C, what is the full name of the nested class A.C A.B.C (Actually, it s C, because the encloser s namespace has nothing to do with the nested class s namespace.) The common language runtime imposes a limitation on the full class name length, specifying that it should not exceed 1,023 bytes in UTF-8 encoding. The ILAsm compiler, however, does not enforce this limitation. Single quotes, should they be used for simple names in ILAsm, are a purely lexical tool and don t make it to the metadata; thus, they don t contribute to the total length of the full class name.

An earlier section ( Class Metadata ) listed the various pieces of information included in a type definition. In the simplest case, when only the TypeDef metadata table is involved, the ILAsm syntax for a type definition is as follows: .class <flags> <dotted_name> extends <class_ref> { ... } The <dotted_name> value specified in the .class directive defines the TypeDef s Namespace and Name entries, <class_ref> specified in the extends clause defines the Extends entry, and <flags> defines the Flags entry.

The numerous TypeDef flags can be divided into several groups, as described here. Visibility flags (binary mask 0x00000007): private (0x00000000). The type is not visible outside the assembly. This is the default. public (0x00000001). The type is visible outside the assembly.

nested public (0x00000002). The nested type has public visibility. nested private (0x00000003). The nested type has private visibility; it is not visible outside the enclosing class. nested family (0x00000004). The nested type has family visibility that is, it is visible to descendants of the enclosing class only. nested assembly (0x00000005). The nested type is visible within the assembly only. nested famandassem (0x00000006). The nested type is visible to the descendants of the enclosing class residing in the same assembly. nested famorassem (0x00000007). The nested type is visible to the descendants of the enclosing class either within or outside the assembly and to every type within the assembly with no regard to lineage. Layout flags (binary mask 0x00000018): auto (0x00000000). The type fields are laid out automatically, at the loader s discretion. This is the default. sequential (0x00000008). The loader shall preserve the order of the instance fields. explicit (0x00000010). The type layout is specified explicitly, and the loader shall follow it. (See 9 for information about field declaration.) Type semantics flags (binary mask 0x000005A0): interface (0x00000020). The type is an interface. If this flag is not specified, the type is presumed to be a class or a value type; if this flag is specified, the default parent (the class that is assumed to be the parent if the extends clause is not specified, usually [mscorlib]System.Object) is set to nil. abstract (0x00000080). The class is abstract for example, it has abstract member methods. As such, this class cannot be instantiated and can be used only as a parent of another type or types. This flag is invalid for value types. sealed (0x00000100). No types can be derived from this type. All value types and enumerations must carry this flag. specialname (0x00000400). The type has a special name. How special it is depends on the name itself. This flag indicates to the metadata API and the loader that the name has a meaning in which they might be interested for instance, _Deleted*. Type implementation flags (binary mask 0x00103000): import (0x00001000). The type (a class or an interface) is imported from a COM type library. serializable (0x00002000). The type can be serialized into sequential data by the serializer provided in the Microsoft .NET Framework class library.