The Power of Lifetimes

This is already expressible in Rust, using invariant lifetimes. You can hand someone an opaque invariant lifetime, let them build a mutable cyclic data structure with it, and then pass that data structure around.

This use of invariant lifetimes, called "generativity," is described in more detail here (https://raw.githubusercontent.com/Gankro/thesis/master/thesi...) in section 6.3, which describes a way to use lifetimes as unique tokens for all sorts of use cases.

And even more closely aligned with what the article is talking about, Catherine West has put together a library that uses generativity to provide a safe interface to a garbage collected heap, as part of a reimplementation of Lua: the `gc-arena` crate in https://github.com/kyren/luster

    int* foo() {
        int i;
        int* p = &i;
        int* q = p;
        return q;
    }

    int* bar(scope int *p); // p doesn't escape bar()
    int* abc(return scope int* p); // p doesn't
       // escape abc() but is returned from it

    int* foo() {
        int i;
        return bar(&i); // ok
        return abc(&i); // error
    }