scala.caps

Carrier trait for capture set type parameters

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.

A type constraint expressing that the capture set C needs to contain the capability R

A trait to allow expressing existential types such as

(x: Exists) => A ->{x} B

The universal capture reference.

An annotation on parameters x stating that the method's body makes use of the reach capability x*. Consequently, when calling the method we need to charge the deep capture set of the actual argiment to the environment.

Note: This should go into annotations. For now it is here, so that we can experiment with it quickly between minor releases