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Attribute Consumers

As you would guess, the .NET 3.5 Framework SDK ships with numerous utilities that are indeed on

the lookout for various attributes. The C# compiler (csc.exe) itself has been preprogrammed to

discover the presence of various attributes during the compilation cycle. For example, if the C#

compiler encounters the [CLSCompliant] attribute, it will automatically check the attributed item to

ensure it is exposing only CLS-compliant constructs. By way of another example, if the C# compiler

discovers an item attributed with the [Obsolete] attribute, it will display a compiler warning in the

Visual Studio 2008 Error List window.

In addition to development tools, numerous methods in the .NET base class libraries are pre-

programmed to reflect over specific attributes. For example, if you wish to persist the state of an

object to file, all you are required to do is annotate your class with the [Serializable] attribute. If

the Serialize() method of the BinaryFormatter class encounters this attribute, the object is auto-

matically persisted to file in a compact binary format.

The .NET CLR is also on the prowl for the presence of certain attributes. Perhaps the most

famous .NET attribute is [WebMethod]. If you wish to expose a method via HTTP requests and auto-

matically encode the method return value as XML, simply apply [WebMethod] to the method and the

CLR handles the details. Beyond web service development, attributes are critical to the operation of

the .NET security system, Windows Communication Foundation, and COM/.NET interoperability

(and so on). 

Finally, you are free to build applications that are programmed to reflect over your own custom

attributes as well as any attribute in the .NET base class libraries. By doing so, you are essentially

able to create a set of “keywords” that are understood by a specific set of assemblies.