What is the reason behind having a StatelessWidget?

Question

I have noticed that, we can use a StatefulWidgetto build any part of the UI without worrying about the state.

What I am asking is simply, what are the reasons behind having a StatelessWidget in the first place, when we can build any UI class as a StatefulWidget whether we are going to provide it with a State or not?

Does using a StatefulWidget comes with an additional cost that makes creating a stateless UI easier/faster/better using a StatelessWidget?

When I read the docs, I can not exactly point out the difference between using StatelessWidget and StatefulWidget when describing stateless UI components. It is even recommended to

Consider refactoring the stateless widget into a stateful widget so that it can use some of the techniques described at StatefulWidget...

Answer 1

If your widget manages state, you should use a StatefulWidget with an associated State object to store the state.

If your widget doesn't manage any state, and its build method only depends on its constructor arguments (or Inherited widgets such as Theme), it's better to use a StatelessWidget. StatelessWidget requires defining fewer classes and invoking fewer methods, so it should be faster and more maintainable than an equivalent StatefulWidget that doesn't cache anything in its state.

If you follow the Push the state to the leaves performance optimization, you will be changing a StatefulWidget to a StatelessWidget and factoring out the stateful parts into a simpler StatefulWidget (which may take a child argument and cache it). This pattern adds more classes but has the benefit of reducing the amount of work necessary when the state changes.