I’m currently working with the Department for Work and Pensions and I’ve found that not everyone means the same thing when they say “reuse”. This has led to me sitting in meetings telling people “this won’t be reusable” to people who think reusable means something different than I.

As I see it we are building a single service that will be deployed once and other services will hook in to it. I’d call that “sharing”, it’s a form of reuse but it’s not the only one. It’s also worth noting that it’s a very hard thing to do.

Types of Reuse

On the recommendation of my team I’ve decided to write down what I see as the different types of reuse and what I think of as suitable language for each type:

Reuse as in Recycle

This is what I mean when I say reuse. As an analogy I have a bottle filled with water. If I drink it all and then fill it up again I am reusing it. In software I can easily give you a duplicate copy of my bottle. So you can reuse my work by filling your copy with water and drinking from it.

In this type of reuse I give you my source code and you deploy another instance of it. It then performs the same way it would for me, perhaps with a few configuration changes to suit your needs.

This is one of the hardest kinds of reuse as it means I need to predict your needs, which is very hard on the first attempt.

An example of this would be most desktop applications, like Google Chrome. With a few configuration changes, like logging in to my Google account, I can reuse the software without having to write it myself.

Summary - Where I build something and you take it and make use of it without much work needed to customise.

Suitable language - Reuse it, deploy it, use it. The emphasis is on you doing something with someone else’s work.

Building on top of it

In this type lets say I’m building a skyscraper. I decide to make it from steel and construct some girders of the lengths I need. I then offer my girders to you so you can build your house. Since your house is smaller you need to make some changes so they suit your needs, such as trimming them to length.

In the software world this is where I publish pieces of my work (say that super awesome Mustache SBT plugin), which you download and make use of in your development as the basis of something else. That may be taking pieces of my code and using that as the foundation of your own components. Or it may be taking entire components and using them in your system.

This is the very foundation of open source development. You still need to do some work but it saves a lot of effort. This is the most useful type in my opinion as it’s the most flexible. And the development world seems to agree as this is how many libraries and tools are built.

Good examples are: Play, SBT, Maven, Dropwizard, Rails, Gatling, Java, Scala, Ruby, Mongo, Postgres, SQL Server that awesome SBT plugin someone wrote… Honestly the list is nearly endless.

Unfortunately this is the type that most “business minded” people dislike. They tend to think that it’s a waste of time to build something, use it to fix your problem, and then let others use it to fix their own problems. They would rather build one thing which fixes everyone’s problems.

The issue with this line of reasoning is you can never fully understand their problems, unless you make them your own.

Summary - Where I build something then you take it and build something else using it.

Suitable language - Extend, build from, build on top of, build out of. The emphasis is on you adding value to my work.

Sharing it

Finally I think this is the last type, at least that I can think of. This is when I build a swimming pool because I want to swim to keep fit. I could publish my specs and designs and lists of building materials but swimming pools are large and expensive. So instead I let you use my swimming pool for your Olympics training, water polo classes, blitsball games, or just to have fun splashing around.

This is by far the hardest type of reuse as I need to fully understand your needs before you start using the thing. That’s a really hard thing to do.

In the swimming pool example I could build myself a small simple pool and be done. To let others use it for their purposes I might need to make it bigger, provide changing rooms, build a diving board, etc. That’s a lot more things I need to do due to the increased number of use cases I have to consider.

It’s also, unfortunately, the type those “business” people love. Because they think you can save effort, by building it once. Obviously this means you save money and effort because their aren’t two teams building so similar things.

I’m not saying it’s a bad thing though, it’s is a very important and often very good thing to do. We only have one internet, one GOV.UK, one Facebook and we all have to share the same one because it would be silly for me to build my own Facebook.

Summary - Where I build something and then let you make use of my instance of it.

Suitable language - Hook in to, connect to, call to, talk to. The emphasis is on you interacting with my instance of the thing.

Focus on the Needs

It should be boring to hear by now but everything you do in Agile should focus on the Needs. For a while I’ve thought that sometimes we focus too often on the users that sit in front of web browsers. Obviously they are important, the most important for a citizen facing service, but they aren’t necessarily the only users.

When building a reusable component, or shared service, or tool for others to build on top of, you’ll have another user. The Developer sitting in front of code trying to use your tool, or the Architect trying to understand your services processes are users too. You need understanding of their context to be able to build anything that will be useful to them.

Which type of reuse you use depends heavily on your user and business needs. Perhaps you are interested in maintaining centralised control of a resource; then sharing might be most appropriate. Or you want to reduce implementation cost of a common piece of work; then reuse might make most sense.

When someone demands that something be a certain type of “reusable” ask them why.

Wrapping up

So as I see it there are 3 things people tend to mean when they say reuse. We should try to get away from using reuse and instead use more specific language for each task.

Reuse Where I build something and you take it and make use of it without much work needed to customise.

Suitable language - Reuse it, deploy it, use it. The emphasis is on you doing something with someone else’s work.

Build on top of - Where I build something then you take it and build something else using it.

Suitable language - Extend, build from, build on top of, build out of. The emphasis is on you adding value to someone else’s work.

Sharing - Where I build something and then let you make use of my instance of it.

Suitable language - Hook in to, connect to, call to, talk to. The emphasis is on you talking to my instance of it.

When someone asks for code to be “reusable” you can point to this and ask “yes, but in what sense?”.