Injection Resolvers

• InjectionResolver
• InjectionResolverFactory
• InjectionResolverFactoryContext
• BuiltInResolvers
• Functions
  • bindResolver
  • unbindResolver
  • hasResolver

All types and functions are exported from the main package:

import {
  BuiltInResolvers,
  bindResolver,
  unbindResolver,
  hasResolver,
  type InjectionResolver,
  type InjectionResolverFactory,
  type InjectionResolverFactoryContext,
} from '@caffeine-projects/dicaf'

An injection resolver is a low-level extension point. When the container resolves a dependency, it picks a resolver factory based on the resolver symbol stored in the InjectionDescriptor, calls the factory to build a resolver function, then calls that resolver to produce the value. Custom resolvers let you plug in resolution strategies beyond the built-in set.

---

InjectionResolver

type InjectionResolver<T = any> = () => T

A zero-argument function that returns the resolved value. The container calls it once per resolution — for singleton scopes that is exactly once; for transient scopes it is once per get() call.

---

InjectionResolverFactory

type InjectionResolverFactory<T = unknown> =
  (ctx: InjectionResolverFactoryContext<T>) => InjectionResolver<T>

A factory that receives context about the injection site and returns an InjectionResolver. Registered with bindResolver() and identified by a unique symbol.

---

InjectionResolverFactoryContext

type InjectionResolverFactoryContext<T = unknown> = {
  readonly container: ContainerOps
  readonly descriptor: InjectionDescriptor<T>
  readonly key?: Key<T>
  readonly kind: 'constructor' | 'property' | 'method'
  readonly member: Identifier
  readonly index: number
}

Passed to every InjectionResolverFactory when the container wires an injection site.

Property	Description
container	The container instance. Use it to call get(), getMany(), or has() during resolver setup.
descriptor	The full InjectionDescriptor for this injection, including key, optional, multiple, and any custom args.
key	The key of the component that declares this injection (i.e. the class that has the dependency, not the dependency itself).
kind	Where the injection appears: constructor parameter, class property, or method parameter.
member	The member name for property and method injections. Empty string for constructor injections.
index	Parameter position for constructor and method injections. -1 when position is not tracked.

---

BuiltInResolvers

const BuiltInResolvers = {
  DEFAULT:  Symbol('dicaf.resolver.default'),
  MAP:      Symbol('dicaf.resolver.map'),
  DEFER:    Symbol('dicaf.resolver.defer'),
  OBJECT:   Symbol('dicaf.resolver.object'),
  PROVIDER: Symbol('dicaf.resolver.provider'),
  VALUE:    Symbol('dicaf.resolver.value'),
} as const

Symbols for the built-in resolver factories. These are the resolver identifiers used by the injection helpers in the Injection reference:

Symbol	Used by
DEFAULT	Plain key injection — the resolver used when no resolver field is set.
MAP	mapped()
DEFER	defer()
OBJECT	object()
PROVIDER	provide()
VALUE	useValue()

---

Functions

bindResolver

bindResolver(name: symbol, factory: InjectionResolverFactory): void

Registers a custom resolver factory under name. Once registered, any InjectionDescriptor whose resolver field matches name will use this factory.

const kUpperCase = Symbol('my-app.resolver.uppercase')

bindResolver(kUpperCase, ctx => {
  const key = ctx.descriptor.key!
  return () => {
    const value = ctx.container.get<string>(key)
    return value.toUpperCase()
  }
})

// use the resolver in an injection descriptor
@Injectable([{ key: ConfigKey, resolver: kUpperCase }])
class Service {
  constructor(readonly label: string) {}
}

Throws ErrResolverAlreadyRegistered if name is already registered.

---

unbindResolver

unbindResolver(name: symbol): void

Removes the resolver registered under name. No-op if name is not registered.

---

hasResolver

hasResolver(name: symbol): boolean

Returns true if a resolver factory is registered under name.

if (!hasResolver(kUpperCase)) {
  bindResolver(kUpperCase, factory)
}