Choosing Our Layers

Categories of layers

We recommend the following software layers:

• Data structures

• A functional core

• Tests

• Boundaries

• Lifecycle

• Workers

Not every project will have all of these layers, but some will. It’s our job as the author of a codebase to decide which layers are worth the price and which ones to eliminate. It’s a lot to remember, so use this sentence as a mnemonic:

Do fun things with big, loud worker bees.

The first letters of the essential words in the sentence match the first letters in our layers:

• Data (do)

• Functional core (fun)

• Tests (things with)

• Boundaries (big)

• Lifecycles (loud)

• Workers (worker bees)

We can see how they all fit together in the following figure: