You are here Home Software Code Reuse

Software Code Reuse

Ad hoc code reuse has been practiced from the earliest days of programming. Programmers have always reused sections of code, templates, functions, and procedures. Software reuse as a recognized area of study in software engineering, however, dates only from 1968 when Douglas McIlroy of Bell Laboratories proposed basing the software industry on reusable components.

Code reuse may imply the creation of a separately maintained version of the reusable assets. While code is the most common resource selected for reuse, other assets generated during the development cycle may offer opportunities for reuse: software components, test suites, designs, documentation, and so on.

The software library is a good example of code reuse. Programmers may decide to create internal abstractions so that certain parts of their program can be reused, or may create custom libraries for their own use. Some characteristics that make software more easily reusable are modularity, loose coupling, high cohesion, information hiding and separation of concerns.

The software library is a good example of code reuse. Programmers may decide to create internal abstractions so that certain parts of their program can be reused, or may create custom libraries for their own use. Some characteristics that make software more easily reusable are modularity, loose coupling, high cohesion, information hiding and separation of concerns.

For newly written code to use a piece of existing code, some kind of interface, or means of communication, must be defined. These commonly include a "call" or use of a subroutine, object, class, or prototype. In organizations, such practices are formalized and standardized by domain engineering, also known as software product line engineering.

The general practice of using a prior version of an extant program as a starting point for the next version, is also a form of code reuse.

Software Code Reuse

Some so-called code "reuse" involves simply copying some or all of the code from an existing program into a new one. While organizations can realize time to market benefits for a new product with this approach, they can subsequently be saddled with many of the same code duplication problems caused by cut and paste programming.

Many researchers have worked to make reuse faster, easier, more systematic, and an integral part of the normal process of programming. These are some of the main goals behind the invention of object-oriented programming, which became one of the most common forms of formalized reuse. A somewhat later invention is generic programming.

Another, newer means is to use software "generators", programs which can create new programs of a certain type, based on a set of parameters that users choose. Fields of study about such systems are generative programming and metaprogramming.

Concerning motivation and driving factors, reuse can be:

• Opportunistic – While getting ready to begin a project, the team realizes that there are existing components that they can reuse.

• Planned – A team strategically designs components so that they'll be reusable in future projects.

Reuse can be categorized further:

• Internal reuse – A team reuses its own components. This may be a business decision, since the team may want to control a component critical to the project.

• External reuse – A team may choose to license a third-party component. Licensing a third-party component typically costs the team 1 to 20 percent of what it would cost to develop internally. The team must also consider the time it takes to find, learn and integrate the component.

Concerning form or structure of reuse, code can be:

• Referenced – The client code contains a reference to reused code, and thus they have distinct life cycles and can have distinct versions.

• Forked – The client code contains a local or private copy of the reused code, and thus they share a single life cycle and a single version.

Fork-reuse is often discouraged because it's a form of code duplication, which requires that every bug is corrected in each copy, and enhancements made to reused code need to be manually merged in every copy or they become out-of-date. However, fork-reuse can have benefits such as isolation, flexibility to change the reused code, easier packaging, deployment and version management.

With thanks to Wikipedia and Scott Adams

Back to the top