Dependency

The Dependency namespace contains constructors and graph combinators.

import {
  Context,
  Dependency,
  build,
  compose,
  merge,
  override,
  provide,
  use,
} from '@fuiste/dependencies'

Constructors

const fixed = Dependency.succeed(Tag, service)
const syncDep = Dependency.sync(Tag, [OtherTag], (context) => service)
const asyncDep = Dependency.async(Tag, [OtherTag], async (context) => service)
const scopedDep = Dependency.scoped(Tag, [OtherTag], async (context) => ({
  service,
  release: async () => {},
}))
const fromExisting = Dependency.fromContext(context)

The requirements array is optional for sync, async, and scoped. Constructors may return raw values or Result values.

Combinators

const graph = compose(config, app)
const parallel = merge(logger, clock, random)
const provided = provide(app, database)
const swapped = override(live, test)

compose carries both sides’ outputs forward. provide satisfies requirements but only exposes the provided dependency’s own outputs. override is the intentional replacement mechanism.

Build

const result = await build(graph)

build returns Result<Context, BuildError>.

Scoped dependencies require:

const scope = Scope.make()
const result = await build(graph, { scope })

Use

const result = await use(graph, async (context) => {
  return runApp(Context.get(context, App))
})

use builds the graph, passes the context to the consumer, closes the scope, and returns a Result for the consumer’s value.

Type Helpers

type Provides = Dependency.Provides<typeof graph>
type Requires = Dependency.Requires<typeof graph>
type Error = Dependency.Error<typeof graph>

These are useful when writing helpers that transform dependency graphs.