Saturday, 11 May 2013

Fixation and variability

While explaining Why Everyone (Eventually) Hates (or Leaves) Maven, Neal Ford divides extensible software into two categories: composable and contextual.

Contextual software is best exemplified by plugin architectures - new features are added by slotting code into explicitly provided extension points. Composable software is best exemplified by the Unix ecosystem - new features are added by wiring together a combination of existing and custom components.

So what is it about contextual systems that provokes such hatred?

The key problem when making software extensible is where to put the variability. I have a fixed set of core features, but I also want others to contribute extra features that vary depending on their needs. How do I bind the fixed and variable functionality together so that they form a coherent system?

Maven accommodates variability like a classic contextual system. The promise (and the curse) of Maven is the consistency of its build lifecycle. There is a place for everything, and everything must be in its place. Maven affords very little flexibility on the relationship between variable additions and its fixed feature set.

Rake, on the other hand, empowers developers by allowing extension via a general purpose programming language. Rake qualifies as a composable system because any means of adding new functionality that can be expressed in Ruby can be used to extend it.

In composable systems, orchestration is variable. In contextual systems, orchestration is fixed. Keeping the means of combination in userland is an additional burden on those who would extend your system, but it's more than offset by the flexibility and power they enjoy in the long term.

Your software will grow, but your relationship with Maven won't. If When that happens, it's time to leave.

No comments:

Post a Comment