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Source Code

The LateBindingApp project is included in the Chapter 16 subdirectory.

Understanding Attributed Programming

As illustrated at beginning of this chapter, one role of a .NET compiler is to generate metadata

descriptions for all defined and referenced types. In addition to this standard metadata contained

within any assembly, the .NET platform provides a way for programmers to embed additional

metadata into an assembly using 

attributes. In a nutshell, attributes are nothing more than code

annotations that can be applied to a given type (class, interface, structure, etc.), member (property,

method, etc.), assembly, or module.

The idea of annotating code using attributes is not new. COM IDL provided numerous prede-

fined attributes that allowed developers to describe the types contained within a given COM server.

However, COM attributes were little more than a set of keywords. If a COM developer needed to

create a custom attribute, he or she could do so, but it was referenced in code by a 128-bit number

(GUID), which was cumbersome at best.

Unlike COM IDL attributes (which again were simply keywords), .NET attributes are class types

that extend the abstract System.Attribute base class. As you explore the .NET namespaces, you will

find many predefined attributes that you are able to make use of in your applications. Furthermore,

you are free to build custom attributes to further qualify the behavior of your types by creating a

new type deriving from Attribute.

Understand that when you apply attributes in your code, the embedded metadata is essentially

useless until another piece of software explicitly reflects over the information. If this is not the case,

the blurb of metadata embedded within the assembly is ignored and completely harmless.

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