OptionalDependency

A marker annotation to indicate that the annotated graph accessor is optional.

If present, the accessor must have a default getter (if it's a property) or function body (if it's a function). If the binding is absent from the graph, the default body will be used. If the binding is present in the graph, this will be overridden and implemented in the graph.

@DependencyGraph
interface AppGraph {
  @OptionalDependency
  val httpClient: HttpClient?
    get() = null

  @OptionalDependency
  fun cache(): Cache? = null
}

If you set the OptionalDependencyBehavior option to REQUIRE_OPTIONAL_DEPENDENCY, this annotation is also required on all injected parameters (even if they already declare a default value). This can be desirable for consistency with accessors and/or to otherwise make the behavior more explicit.