Can you use refactoring to build a framework?

It's a common question, and the short answer is that yes, refactoring is very useful when building a framework. But the issues involved depend on the state of life of the framework, and particularly in the approach you use to building a framework.

The common issue in the mind of someone who has this question is that users of a framework need a stable interface to work against. Any changes to an interface can have severe ripple effects. In my terminology, a framework usually has a Published Interface. Published interfaces are usually a pain for refactoring because any refactoring that changes a published interface is made much more difficult.

One reason this is less of an issue is because many refactoring that you might do to a framework don't affect the published interface. Within the non-published boundary, you can refactor freely. Sadly languages usually don't allow you to mark published interfaces very cleanly, so you'll usually have to do some extra work to set up a properly published section to your interface.

Styles of Framework

The role of refactoring has a lot to do with how you build your frameworks. Many people have the notion of a FoundationFramework. In this case you have to fix and publish your API as soon as possible, which means that refactoring is less useful due the limits I mentioned above.

But a FoundationFramework isn't necessarily the best way to go. I've seen a lot of failures in building frameworks that way. I think HarvestedFramework is a much better way to go, and refactoring is extremely useful when you are building a HarvestedFramework.