When I build an application, I build frameworks along the way. I recently realized that not everybody thinks this is normal, so I thought I'd give a description of what I do and why I think it's a good idea.
But let's stop for a moment and briefly discuss what I understand to be a software development framework. Examples of frameworks are frontend web frameworks like React, backend web frameworks like Django, UI component frameworks like Ant Design, an ORM like SQLAlchemy, or a form library like mstform (which I helped create), and so on.
A framework can be large or small, but in the end it's code that fulfills some task that you can control by plugging in your own code and declarations. Frameworks are declarative in nature, and declarations tend to be easier to understand and maintain than code that has a lot of moving imperative parts. This way frameworks also help you structure your application. My article Framework Patterns discusses a bunch of ways frameworks let you do that.
I will fully admit my bias up front: I like creating frameworks. But besides enjoying it, I also think this activity has enormous benefits when you build large, long-lived, successful applications.
Examples are good! Over the last two decades, I've written or helped to write the following "roll your own" frameworks while building applications:
Why a framework at all?
Frameworks are overhead. You need to learn them. They can be in the way. They may have performance implications.
Why not just avoid them altogether? Use the platform, whether that may be the web browser or the operating system or whatever else.
I think this is an illusion. A platform is already a framework. If it fits what you want to do, great. But it may just not be a great framework for your particular purpose.
Frameworks offer features and help you get things done.
A more subtle effect is that frameworks also help with maintenance -- they offer a structure to your application code that makes it easier to decide how to add new features to it and makes it easier to navigate your codebase.
Successful applications tend to grow in complexity over time. Frameworks can help you prevent your application from growing into a big ball of mud.
Why aren't existing frameworks enough?
Why should you roll your own frameworks at all and not just build on top of an existing one? After all, an existing popular framework has many benefits: it is documented, you can hire people that already know it, and perhaps most importantly, you don't have to build and maintain it yourself. Even if you pick a less popular framework it still means you don't have to build and maintain it, and there is so much out there.
All this is true, and I encourage people to use existing frameworks where possible. But as everyone who has used a framework knows, you tend to reach points where the only way to make a framework do what you want is an ugly way. This is not a surprise -- all applications and all developers are unique, and a framework tries to generalize concerns, so it's likely it doesn't fit perfectly all the time.
That's usually okay -- you often gladly pay the price of more work in exchange for the feature the framework offers. But sometimes it's not okay; sometimes the price you have to pay to write nice code is too high -- it's difficult to write, it's hard to test, or the maintenance burden is enormous.
Small versus large
Small frameworks that do one thing well tend to be less constraining than larger frameworks that arrange a whole set of things for you. A web framework like Django offers a whole bunch of features out-of-the-box: from templating to database integration, all in an integrated whole. Because Django makes these choices, a development team does not have to make them. Removing the burden of decision making alone can be valuable, so you can focus on what is important. But it also makes it more likely that some of the choices do not fit what your application needs.
A smaller web framework, like Flask (or Morepath, which I created) does less, but also gives the developers more room to make the right decisions for the application. It's a trade-off.
The choice to remain focused can have an impact on the ecosystem surrounding a framework. React chose to remain focused. As it became more popular, a lot of creative solutions to other problems emerged in its ecosystem: forms, state management, UI component libraries, routing, and much more. If React had made these choices for the developers, there might have been less room for this creative ferment. But it does load up developers with extra choices to make, such as whether they should use Redux, Mobx or something else.
Mind the gaps
No matter which frameworks you choose to use, there will be gaps. There will be important functionality of your application where your existing framework doesn't have an opinion and you can find no smaller framework to help you in a satisfactory way. The price you have to pay for just "powering through" by doing a repetitive ugly thing is too high -- the code becomes unmaintainable or even impossible to write correctly. This may be tolerable for minor features, but unfortunately it's most likely to happen in core features of your application, where you spend the most effort. What to do then?
Roll your own
That's when I start thinking about rolling my own framework. I focus my own framework on exactly the problems the application needs help with the most. The benefit is that I can decrease the maintenance cost of the application code and accomplish difficult goals. The cost is that I need to write and maintain the framework.
I think people often underestimate the benefits of doing this and overestimate the costs, so I will discuss both.
The benefits are the same as you get from any framework. Your custom framework helps organize your code in structures that help with maintenance, and makes hard things easier. Your own framework is likely to fit your application's concerns pretty well. Another big benefit is that if it turns out the framework needs new features, you don't need to wait for anyone and can just add them.
Application code tends to be difficult to test automatically. This is because an application by its nature tends to integrate things -- servers, file systems, databases, and so on. It's a whole. This means that application tests tend to lean towards integration tests, and integration tests are harder to write, slower to run, and more difficult to maintain than subsystem tests.
But the code of your framework is not application code and does not suffer from these problems. It's a subsystem. Tests tend to be easier to write and maintain and they can run quickly. So by creating a framework for application functionality you have taken that functionality out of the difficult and frustrating to test realm and put it into the fun and easier to test realm.
Because you have separated the framework from the rest of the functionality, it becomes easier to ensure loose coupling between the framework and the application. Loose coupling and tests allows you to move very quickly in a framework codebase, and make changes that can have a big impact right away throughout your application.
It's also easier to document a framework. This is because you have something separate you can point at that is not enormous and therefore not overwhelming to document.
All of these things incidentally tend to become easier if you separate your framework into its own software package and maintain it separately from the application, though this also has drawbacks -- you need to manage these packages -- so decide whether you should do this on a case-by-case basis.
All this means that the maintenance burden of your framework is less than you might expect -- if you extract a framework from your application you can effectively convert a larger maintenance burden in your application to a smaller one in your framework.
But you still need to create the framework. Is this something super difficult that only elite genius programmers can do? It would be cool to think so as this would mean I'm an elite genius programmer, but I actually think framework creation should and can be part of the toolbox of any developer. It's something that you can learn.
The act of creating a framework may seem daunting, but a framework can be tiny and still be worthwhile. Many frameworks fit in a single screen of code.
Here are some things that may well fit in one screen of code and are frameworks:
a reusable HTML template.
a base class.
a React component with an onClick event handler.
a function that takes another function as an argument.
Examples of tiny frameworks I've helped to create, just in the last few months, include:
a way to define how to export and import fields of a particular data model to and from Excel.
a small wrapper to make it easier to talk to particular SOAP endpoints.
a way to use this wrapper to make it easier to write testing mocks for SOAP endpoints.
a Python decorator to declare certain common authorization behaviors more easily.
integration between URLs and form state to make it easier to express complicated search parameters.
You will note that I have a harder time describing these tiny frameworks as I can't just say "backend web framework" or "form library", which immediately call up a whole bunch of associations for many people. That's because these frameworks were designed to serve very specific goals.
Here are two slightly bigger frameworks I've built to help serve application-specific goals:
a frontend store that integrates an existing React Table component with a backend REST service. It takes care of synchronizing pagination, searchability, sortability, and manages frontend URL parameters.
a customizable way to normalize frontend JSON payloads and backend data where some fields are read-only for security purposes.
Again you will note it is more difficult to express what I mean. As long as you can define what they do well for yourself and the people who use them, that may actually be a good thing. It means you're solving real problems for a specific application.
Incidentally I could not describe my front-end web framework Obviel very well in the beginning, as people weren't very familiar with those ideas yet -- it was before Backbone, Ember, Angular, React and Vue came along. Now it's easy.
How to grow your frameworks
I won't go into the technical details of how to create a framework here. Look at existing frameworks for guidance, and read my Framework Patterns article. Instead I want to discuss ways to incrementally create frameworks while you build an application.
Certainly do not try to build a grand unifying framework that will solve everything once it is done. This is a trap. It will result in analysis paralysis or over-engineering. You risk solving problems you don't actually have and blinding yourself to the problems you do need to solve. Do not make the construction of a framework a requirement for the construction of the application that needs it.
When I say create frameworks when you build an app I do mean multiple frameworks. By all means don't start from scratch. Build on existing frameworks. When you have a particular problem and you suspect someone else has solved it already, look around first.
I try to stop myself from building a larger framework if I already know existing frameworks are out there that solve a similar problem. Only after due consideration of these do I start thinking about rolling my own. For tiny frameworks this doesn't matter that much, as they're very fast to create anyway.
If you are very experienced in a particular problem domain you may be able to build a framework independently of constructing applications that need it. But that is the exception to the rule: in general you should not build a framework before you are building the part of the application that needs it.
Look for opportunities
You won't know about all the frameworks you need to build when you start building your application. Just iteratively build application features. But keep your eye out for framework opportunities: that bit of code that is repetitive and annoying. General rule: repetitive (mostly) declarative code is fine, but repetitive imperative code is a risk and thus an opportunity for a framework that can help make it more declarative.
Then build a modest framework to help you. Integrate it with the application early.
When you integrate a framework into an application, first tackle a single case, and then spread it out to all the other places you can use it. So try your validation system with a single form first, tweak it where needed, and then spread it to all the other forms, tweaking it as you go.
Make sure to spend time to convert existing code to use the framework you created. This can give you insight about gaps in your framework you may want to fix. The consistency is important. Programmers look for example code in the application first. Make sure all existing code uses the new pattern so that the old way of doing things that doesn't use the framework yet doesn't spread inadvertently.
Look for opportunities for growing existing frameworks. Your form validation library could perhaps automatically clear invalid fields or set defaults in the same validation phase. And since you have spread it to all forms already, now it is easy to add this new functionality everywhere in your application all at once.
Pretend a little
Don't worry too much about whether your framework is useful in another context. It's already useful if it helps you in a single application. But do pretend a little to yourself that you will open-source it. Have good tests and write documentation and a changelog. The future will be grateful.
But because you didn't open-source it or since your open source project has 1.5 users (like most of mine!) don't be too afraid to break APIs in the early days if you need it. Mold them like the wet clay they are.
Use existing frameworks where you can, but don't be afraid to roll your own when you can't. It may seem daunting but it can be learned. By extracting a framework both your application and the framework can become easier to manage.
So next time you are working on an application, look for framework opportunities. Don't be too ambitious, but start small, then slowly grow your framework. It's great to give it the open source treatment with tests, documentation and a changelog, but it doesn't have to be in set in stone right away because of that. It's your own framework and you can make it do what you need, even if you change your mind along the way.
So plant a few framework seeds in the garden of your application, and have fun!
Thank you to those who generously helped to proofread this article: