If you are reading this tutorial in order, you’ve just finished the reference capabilities chapter and your brain probably hurts. We’re sorry about that. Hopefully object capabilities, while a new concept, are less mind bending.

We touched on object capabilities previously in the tutorial, this chapter will dig in more. So, what is an object capability?

A capability is the ability to do “something”. Usually that “something” involves an external resource that you might want access to; like the filesystem or the network. This is called an object capability. Object capabilities have appeared in a number of programming languages including E.