Capability

Base trait for classes that represent capabilities in the object-capability model.

A capability is a value representing a permission, access right, resource or effect. Capabilities are typically passed to code as parameters; they should not be global objects. Often, they come with access restrictions such as scoped lifetimes or limited sharing.

An example is the Label class in scala.util.boundary. It represents a capability in the sense that it gives permission to break to the enclosing boundary represented by the Label. It has a scoped lifetime, since breaking to a Label after the associated boundary was exited gives a runtime exception.

Capability has a formal meaning when Capture Checking is turned on. But even without capture checking, extending this trait can be useful for documenting the intended purpose of a class.