From a management point of view, reuse is obviously a no-brainer. When you view development as manufacturing (fast forward to 20:30), reuse looks a lot like replacing a human assembly workflow in the production of your widget with a mechanized one - you gain speed and reduce variability and error rate. The return on investment is clearly fantastic.
I have a vision in my head of a meeting taking place between IT professionals and upper-middle management at a technology-related company sometime in the 70's, maybe the 80's, as they are about to break ground on a new application.
Exec: "... Alright then, let's design and build it. Get to work."
IT Pro: "You know, if we are careful to keep these functions separate and generic, I think we could reuse them for other purposes later.
Exec: "You can... reuse them? Like, take code from one application and plug it into another? For free?"
IT Pro: "Absolutely. Like your golf clubs - you don't have a separate set of clubs for the 5 private courses you belong to, you take the same set of clubs to each one. A set of clubs is designed to be flexible and accommodating."
Exec: "Well this is a great idea. We need more of this. This is the norm from now on - I expect to see you start reusing everything."
Management was excited because their scorecard numbers were going to go up. The developers were excited because they got a mandate to build beautiful things. And thus was born the fallacy that internal code reuse is free, easy, and something we should be doing all the time.
As a learning exercise, I took one chunk of functionality from one of our applications I'm working on and set about making a crisp, clean, fully reusable WCF service out of it. I wanted to see the result from a purely technical standpoint - I didn't really care about the potential return on investment, I just wanted to see if I could work through the little fiddly things that make a service ugly and tightly coupled unless you clean them up.
From a technology point of view, I'm happy with the result and learned a lot about making a great service. It took a while, even though it only provides a very discrete bit of functionality, but it's shiny and beautiful. It's even got documentation. I can use what I learned in the future, even on services that I don't intend to be reusable, to make them clean and easy to use.
The real learning, though, took place after I finished, while I was reflecting on my sparkling work and started to ask myself what I now realize are the most important questions.
- Who is ever going to need this functionality?
- If they need it, how likely is it that they're going to find out about this code I wrote, even if they're in my same organization?
- If they find out about it, how likely is it that they're going to want to spend the time reading the documentation to figure out how to use it? (From a more general perspective, it's a stretch to assume that there's documentation in the first place).
- If they read the docs, how likely is it that they're still going to want to use it when they realize it's going to need additional features to support their needs?
- If they still want to use it, how likely is it that they're actually going to jump through the organizational hoops to get access to the code, do development on my code to add features (or get me to do it) in a way that keeps it reusable (difficult and time-consuming), and ensure that the new version can be deployed without messing up the application that currently uses it?
All that for one small piece of functionality. That funnel is pretty narrow at the top and tapers to the width of a hair at the end. Reuse is supposed to be a best practice; it's supposed to make your arsenal of applications clean and organized, and reduce the amount of work you need to do. Why does reuse all of a sudden look so difficult and expensive in light of these questions?
The answer: Internal reuse trades one kind of technical work for another that's just as difficult if not more, and adds extra organizational work on top. The new work that you've bought yourself is the most nefarious kind: the kind that looks like it's free. The kind that ends up as estimate line-items with .5 hours because they have to be in the project plan, but they won't result in new deliverables, so they must require no effort. Even worse, this cost isn't only paid the first time a component is reused - it's paid every time it's reused. At least when it comes to reuse of internal code (as opposed to third party controls and frameworks), I believe that Not Invented Here syndrome is less of an unwillingness to adopt work from another culture and more of a subconscious rejection of this new work that we know we are generating, but can't quite put our fingers on.
The technical work being traded out is new development. Everyone knows that the best code is no code, or perhaps more appropriately in this case, code written by someone else who must be smarter than the herd of cats that is your current development team, so wiping new development off of the project plan looks great.
There's no such thing as a free lunch, though. First, let's look at the code we're thinking about reusing. To be worth reusing, code has to solve just about every aspect of a very distinct and common problem from just about every angle, be well encapsulated, be distributed in a way that supports reuse, and above all, it must be hard to create. Really hard. If you want to benefit from its reuse, solving the new technical and organizational problems that reuse introduces must be easier than initially creating it.
The only way code can hit all those criteria is if it's developed away from a project that's going to be using it. It has to be its own effort, and that effort has to involve looking at (and testing) lots of different scenarios and use cases, not just the one that your new app needs and that you think some other apps are going to need later. It doesn't have to start off that way, but it has to end up that way before it's truly reusable. Reusable components aren't parts of projects, they are projects. Unfortunately, developing a component in isolation that doesn't solve a full business problem, but might solve a part of multiple common problems, almost never looks like a good short-term investment, and thus almost never happens.
Now, without knowing yet if this old code you're looking at can really solve your problem, your team, Team ABC, now has the job of understanding and using someone else's software, arguably the second-most reviled task in development. To misquote jwz, "Some people, when confronted with a problem, think 'I know, I'll reuse some code we already have.' Now they have two problems." Unlike a lot of other industries, in software development, understanding and leveraging someone else's work is often actually harder than producing your own.
So, flush some design hours down the drain, and what's the result? The ABC designers come back and say, "This almost solves our problem. It needs features X, Y and Z." Now they've got to add features onto existing code someone else wrote, arguably the first-most reviled task in development, and certainly one of the hardest. This is where the organizational problems, which began well before your project was set in motion, start to clearly manifest themselves.
The code that ABC wants to add features to and reuse was written by Team 123. Team 123 isn't a permanent team; it was assembled for a project two years ago. Three of its members have moved on to other organizations. No one knows where the documentation is, how good it is, or if there was any to begin with. There are three code bases scattered throughout source control and no one's sure which one's the golden one. Furthermore, no one is sure which applications are using the component in question, and which quirks they rely on, so the potential for making breaking changes is high.
And this all assumes that Team ABC had heard of Team 123's code in the first place. In an organization of any size, unless you have a full-time "code reuse librarian" (you don't), the chances of this are virtually nil.
In the end, what it comes down to is that your problem probably isn't common enough or hard enough to warrant development of a reusable component, and you probably don't have the budget or time to put in enough work on something to make it reusable when it doesn't fully solve a business problem by itself. By all means, make your code beautiful. Design it in a loosely-coupled, encapsulated fashion, because it will be easier to maintain. Just remember that while reusable code is loosely coupled and well-encapsulated, loosely-coupled and well-encapsulated code isn't necessarily reusable. Reusability is a meta-feature, and if you want your code to be reusable, you have to design and build all of it around that. Don't try too hard to reuse code or create reusable code - focus on solving business problems.
Side note on SOA: SOA aims to reduce the organizational problems caused by reuse. It does not address the technical ones, nor does it preclude the need to spend extra time developing truly reusable components. In fact, it mandates it - you can't have SOA without solid, reusable code.
One more side note: Interestingly, a Google search on "code reuse" without any adjectives or qualifiers pulls the following three articles on the first results page: