If you were a software developer in the 1990’s or 2000’s, software reuse was kind of like the Holy Grail.
You probably thought it was a good idea in theory from the start. Plus, managers were always enthusiastic about wanting to get more of it.
But achieving software reuse in practice was, and still can be, difficult. It’s one thing if you can use really stable, trusted code libraries and treat them as black boxes in your code. Unfortunately this only works if those black boxes don’t run into problems, even when you deploy them on hardware that’s different than what the original writers used. (Good luck.)
Here’s why I think software reuse is difficult.
First, we need to note the difference between explicit knowledge and tacit knowledge. Explicit knowledge is what you get from books, or memos, or hearing a story or experience that someone else shares with you. Tacit knowledge is what you get from experimentation, mentorship, or exploration. (For example, I have no explicit knowledge of the vi editor – but I have extensive tacit knowledge of it, because when I open the editor my fingers know what to do, darting back and forth between ESC and : and other punctuation marks that my brain is not consciously processing. Perl is kind of the same way for me.)
If software is the executable representation of knowledge, then developing software is the process of codifying (literally!) tacit and explicit knowledge to make it executable. That’s a huge challenge that requires the developer to learn, reflect, experiment, learn, reflect, experiment… and so on. It’s a process of learning that ultimately results in software – a tool that hopefully will earn a life of its own, perhaps extending beyond the time that the original developer works on it.
What do you get by reading and exploring someone else’s code? Explicit knowledge. What do you get by writing code yourself, by uncovering each new function one at a time, by realizing you didn’t know what you were doing the first time, by refactoring, by trying out a new design (or maybe two or three), by bouncing ideas off of your colleagues, or by going back to the first design you had a long time ago? That’s tacit knowledge. You need both to write good software.
Unless there’s some way to get that tacit knowledge of someone else’s code, or you don’t need the tacit knowledge anyway (ie. in the case of the “black box”), successful reuse will be challenging… if not impossible.
(Related Post –> Software Reuse Antipatterns)