4.1 Object Oriented Code Reuse

4.1 Object Oriented Code Reuse

Code reuse has been a goal for computer scientist for decades now. Part of the promise of object oriented programming is flexible and advanced code reuse. The CLR is a platform designed from the ground up to be object oriented, and therefore to promote all of the goals of object oriented programming.

Today, most software is written nearly from scratch. The unique logic of most applications can usually be described in several brief statements, and yet most applications include many thousands or millions of lines of custom code to achieve their goals. This can not continue forever.

In the long run the software industry will simply have too much software to write to be writing every application from scratch. Therefore systematic code reuse is a necessity.

Rather than go into a lengthy explanation about why OO and code reuse are difficult-but-necessary, I would like to mention some of the rich features of the CLR that promote object oriented programming.

· The CLR is an object oriented platform from IL up. IL itself includes many instructions for dealing with memory and code as objects.

· The CLR promotes a homogeneous view of types, where every data type in the system, including primitive types, is an object derived from a base object type called System.Object. In this respect literally every data element in your program is an object and has certain consistent properties.

· Managed code has rich support for object oriented constructs such as interfaces, properties, enumerated types and of course classes. All of these code elements are collectively referred to as types when referring to managed code.

· Managed code introduces new object oriented constructs including custom attributes, advanced accessibility, and static constructors (which allow you to initialize types, rather than instances of types) to help fill in the places where other object oriented environments fall short.

· Managed code can make use of pre-built libraries of reusable components. These libraries of components are called managed Assemblies and are the basic building block of binary composeability. (Reusable components are packaged in files called assemblies, however technically even a managed executable is a managed assembly).

· Binary composeability allows your code to use other objects seamlessly without the necessity to have or compile source code from the third party code. (This is largely possible due to the rich descriptions of code maintained in the metadata).

· The CLR has very strong versioning ability. Even though your applications will be composed of many objects published in many different assemblies (files), it will not suffer from versioning problems as new versions of the various pieces are installed on a system. The CLR knows enough about an object to know exactly which version of an object is needed by a particular application.

These features and more build upon and extend previous object oriented platforms. In the long run object oriented platforms like the .NET Framework will change the way applications are built. Moving forward, a larger and larger percentage of the new code that you write will directly relate to the unique aspects of your application. Meanwhile, the standard bits that show up in many applications will be published as reusable and extendible types.