A Layer as constructor

A Layer describes how to build a service and supply its dependencies. A service is the named interface callers use for a job.

Sam compares the constructor pattern to a Layer and uses a React component as an analogy. In the same discussion, he connects the pattern to infrastructure policies. Watch from 18:45.

See Sam Goodwin on Alchemy10 and cartridges36.

Read why dependency injection matters14.

Sources

  1. Sam Goodwin - Alchemy - YouTube. Sam Goodwin. Layer composition discussion; used for infrastructure carried with a service. Accessed 2026-10-01.

Last changed 2026-10-07 in e73c9d9. Source on GitHub. Change log.

Linked from

  1. A service captures its construction dependencies. Build a service with its dependencies, then expose methods that callers can use without rebuilding the graph.

    See also: domain structure, Layer composition, the Layer constructor pattern, and testing through services.¶

  2. Agent guide. An Effect stack so pure (aspirational) Kit Langton will blush.

    A Layer as constructor — Sam Goodwin compares an Effect Layer that builds a service to a constructor.

  3. Change log. What changed in the files served here, newest first.

    A Layer as constructor — edited: feat(learn): teach the next twenty cards with plain lines, diagrams and snippets

  4. Code snippets quote a pinned source. Shipped design brief: pinned Git objects, typed diagnostics, and one build-only snippet model for both views.

    Layers provide the adapters.

  5. Dependency injection is the reason to choose Effect. Effect tracks service requirements in types and supplies replaceable implementations through Layers.

    Read the Layer constructor pattern.¶

  6. Engine-neutral tokens keep adapters replaceable. The highlighter port exposes text, roles, and font styles rather than Shiki types.

    Both adapters provide the same port through an Effect Layer.¶

  7. Full agent guide. An Effect stack so pure (aspirational) Kit Langton will blush.
  8. Hexagonal architecture. Ports name the application's jobs; adapters connect them to the outside world.

    A Layer as constructor explains the construction mechanism.¶

  9. learn-rat-stack. Trace a capability through Effect, XState, five projections, the CLI, and Alchemy. Try hosted search and read.

    The service exposes its Layer beside the implementation.

  10. Rat Stack lore | rat-stack. Short, source-grounded notes on the ideas and decisions behind rat-stack.

    A Layer as constructor — Sam Goodwin compares an Effect Layer that builds a service to a constructor.

  11. rat-stack. An Effect stack so pure (aspirational) Kit Langton will blush.
  12. Source change history (log.md). The generated change log as Markdown.

    A Layer as constructor — edited: feat(learn): teach the next twenty cards with plain lines, diagrams and snippets