Gems are great...
Gems are a superb tool for every Rubyist. They can help you rapidly implement complex solutions in your applications without having to reinvent the wheel.
The very rich ecosystem of gems can provide you with basically any functionality you could think of: authorization, admin panels, pagination – you name it.
...but not when overused
One could think that you can't go wrong with something as useful as gems. Yet, careless addition of new gems might be harmful in the long run.
Adding too many gems to your application might cause several problems. Some of them are more immediate while others might show up later on in application's lifecycle.
To code or not to code
One of the reasons to use gems is to not reinvent the wheel – someone already wrote some code which tackles the problem at hand. In some cases it's instead worth to code the functionality yourself.
One case is when the needed functionality is simple enough that it won't take you more than 30-60 minutes to create.
Other case would be when the solution needed in the project is very specific and no gem would be able solve it without modifications.
With each new gem added to your application, your application's process will grow larger and larger, consuming more server resources and slowing response and startup times.
Each gem also brings it's dependencies to your application, making your application's size grow faster than you might expect.
Gems just work and you don't really know how in order to use them. It's often enough when you're on tight deadlines in your projects.
But if you strive to be a better programmer and really understand the code you're writing, it's a good idea to take a look at how gems you use work.
High reliance on gems might also make getting familiar with the project more difficult, especially if someone isn't used to gems included in the project.
Updating gems sounds easy – but when you're using many gems with a lot of dependencies it might become a nightmare.
Different gems, depending on their update schedules, might become incompatible with one another after some time, due to being dependent on different versions of the same gems.
Monkey patching those incompatibilities or trying to replace the incompatible gems – either by other gems or own code – is something most developers would prefer to avoid.
Except already mentioned incompatibilities due to gem dependencies some gems might be just incompatible due to similar functionality they provide. If the code in those gems gets in each other's way those gems probably won't work well together.
Like before, you might be able to find workarounds to make them work, but it's best to just avoid them if possible.
Gems are a great tool – but like every tool, they can be used irresponsibly.
If you need some basic guidelines, you might try answering some questions before adding a new gem to your app.
Does the gem you want to add:
- Provide functionality simple enough to be implemented without a gem?
- Meet all the specific functionality requirements needed by the application?
- Bring overhead worth functionality it provides?
- Have an active maintainer?
I'm not saying you should abandon using gems – only to be more conscious about it.