OptionalBinding

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

On Graph Accessors

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 {
  @OptionalBinding
  val httpClient: HttpClient?
    get() = null

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

On Injected Parameters

If you set the OptionalBindingBehavior option to REQUIRE_OPTIONAL_BINDING, this annotation is also required on all injected parameters (even if they already declare a default value) for @Provides declarations or @Inject constructors/top-level functions.

This can be desirable for consistency with accessors and/or to otherwise make the behavior more explicit.