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The Necessity of Type Metadata

The ability to fully describe types (classes, interfaces, structures, enumerations, and delegates)

using metadata is a key element of the .NET platform. Numerous .NET technologies, such as object

serialization, .NET remoting, XML web services, and Windows Communication Foundation (WCF),

require the ability to discover the format of types at runtime. Furthermore, cross-language interop-

erability, numerous compiler services, and an IDE’s IntelliSense capabilities all rely on a concrete

description of type.

Regardless of (or perhaps due to) its importance, metadata is not a new idea supplied by the

.NET Framework. Java, CORBA, and COM all have similar concepts. For example, COM type

libraries (which are little more than compiled IDL code) are used to describe the types contained

within a COM server. Like COM, .NET code libraries also support type metadata. Of course, .NET

metadata has no syntactic similarities to COM IDL.

Recall that the ildasm.exe utility allows you to view an assembly’s type metadata using the

Ctrl+M keyboard option (see Chapter 1). Thus, if you were to open any of the *.dll or *.exe assem-

blies created over the course of this book (such as the CarLibrary.dll created in the previous

chapter) using ildasm.exe and press Ctrl+M, you would find the relevant type metadata (see

Figure 16-1).

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Figure 16-1.

Viewing an assembly’s metadata

As you can see, ildasm.exe’s display of .NET type metadata is very verbose (the actual binary

format is much more compact). In fact, if I were to list the entire metadata description representing

the CarLibrary.dll assembly, it would span several pages. Given that this act would be a woeful

waste of paper, let’s just glimpse into some key metadata descriptions of the CarLibrary.dll

assembly.