Throughout this book, I have emphasized that a .NET application contains code, data, and metadata. Metadata is information about the data—that is, information about the types, code, assembly, and so forth—stored along with your program. This chapter explores how some of that metadata is created and used.
Attributes are a mechanism for adding metadata, such as compiler instructions and other data about your data, methods, and classes to the program itself. Attributes are inserted into the metadata and are visible through ILDASM and other metadata-reading tools.
Reflection is the process by which a program can read its own metadata, or metadata from another program. A program is said to reflect on itself or on another program, extracting metadata from the reflected assembly and using that metadata either to inform the user or to modify the program's behavior.
An attribute is an object that represents data you want to associate with an element in your program. The element to which you attach an attribute is referred to as the target of that attribute. For example, the attribute:
is associated with a class or an interface to indicate that the target class should derive from
IUnknown rather than
IDispatch when exporting to COM. I discuss COM interface programming in detail in Chapter 23.
Some attributes are supplied as part of the CLR, or by the framework. In addition, you are free to create your own custom attributes ...