Capabilities

Reading

• ⭐ Context Capabilities - tmandry

  Discusses the addition of a context system in Rust. with keyword for functions and traits implementations.

  Matches what I had in mind for a capability system. It is possible to make capabilities no-cost by using ZSTs.

  Implementation passes context as extra function arguments.

• Designing with Static Capabilities and Effects: Use, Mention, and Invariants

Samples

struct Env; // ZST. impl uses a global type
struct BasicArena { }

#explicit capability env = Env; // capability use-case
#implicit capability arena = BasicArena; // context use-case

fn std::env::var(s: AsRef<str>) String with Env {}
fn std::env::var(s: AsRef<str>) String with Env {}

fn main() () \ {env} {
  let arena = BasicArena.new();
  use arena as Arena;

  foo()
    // pass some capabilities explicitly
    .with(Env)
}

fn foo() uint \ {arena, env} {
  let id = arena.alloc(1);
  let var = std::env::var("foo")?;
}