Question

It is straightforward to copy-paste code to achieve repetitive actions, what is the downside of such an approach?

Answer 1

Copy-and-paste programming, sometimes referred to as just pasting, is the production of highly repetitive computer programming code, as produced by copy and paste operations. It is primarily a pejorative term; those who use the term are often implying a lack of programming competence. It may also be the result of technology limitations (e.g., an insufficiently expressive development environment) as subroutines or libraries would normally be used instead. However, there are occasions when copy-and-paste programming is considered acceptable or necessary, such as for boilerplate, loop unrolling (when not supported automatically by the compiler), or certain programming idioms, and it is supported by some source code editors in the form of snippets.

Repetitive tasks or variations of a task

One of the most harmful forms of copy-and-paste programming occurs in code that performs a repetitive task, or variations of the same basic task depending on some variable. Each instance is copied from above and pasted in again, with minor modifications. Harmful effects include:

• The copy and paste approach often leads to large methods (a bad code smell).

• Each instance creates a code duplicate, with all the problems discussed in prior sections, but with a much greater scope. Scores of duplications are common; hundreds are possible. Bug fixes, in particular, become very difficult and costly in such code.

• Such code also suffers from significant readability issues, due to the difficulty of discerning exactly what differs between each repetition. This has a direct impact on the risks and costs of revising the code.

• The procedural programming model strongly discourages the copy-and-paste approach to repetitive tasks. Under a procedural model, a preferred approach to repetitive tasks is to create a function or subroutine that performs a single pass through the task; this subroutine is then called by the parent routine, either repetitively or better yet, with some form of looping structure. Such code is termed "well decomposed", and is recommended as being easier to read and more readily extensible.

• The general rule of thumb applicable to this case is "don't repeat yourself".