Interface Nesting

🚧 Status: Currently only contracts and contract interfaces support nested interfaces.

Interfaces can be arbitrarily nested. Declaring an interface inside another does not require implementing types of the outer interface to provide an implementation of the inner interfaces.

// Declare a resource interface `OuterInterface`, which declares
// a nested structure interface named `InnerInterface`.
//
// Resources implementing `OuterInterface` do not need to provide
// an implementation of `InnerInterface`.
//
// Structures may just implement `InnerInterface`.
//
resource interface OuterInterface {

    struct interface InnerInterface {}
}

// Declare a resource named `SomeOuter` that implements the interface `OuterInterface`
//
// The resource is not required to implement `OuterInterface.InnerInterface`.
//
resource SomeOuter: OuterInterface {}

// Declare a structure named `SomeInner` that implements `InnerInterface`,
// which is nested in interface `OuterInterface`.
//
struct SomeInner: OuterInterface.InnerInterface {}