[][src]Crate topo

topo creates a hierarchy of nested scopes represented as stable identifiers referring to the function callgraph.

Each scope in this hierarchy has a unique and deterministic crate::Id describing that environment and the path taken to arrive at its stack frame. These identifiers are derived from the path taken through the callgraph to the current location, and are stable across repeated invocations of the same execution paths.

By running the same topologically-nested functions in a loop, we can observe changes to the structure over time. The moxie crate uses these identifiers and environments to create persistent trees for rendering human interfaces.

Making functions nested within the call topology

Define a topologically-nested function with the topo::nested attribute:


fn basic_topo() -> topo::Id { topo::Id::current() }

fn tier_two() -> topo::Id { basic_topo() }

// each of these functions will be run in separately identified
// contexts as the source locations for their calls are different
let first = basic_topo();
let second = basic_topo();
assert_ne!(first, second);

let third = tier_two();
let fourth = tier_two();
assert_ne!(third, fourth);
assert_ne!(first, third);
assert_ne!(first, fourth);
assert_ne!(second, fourth);



A value unique to the source location where it is created.


Identifies an activation record in the current call topology.


The root of a sub-graph within the overall topology formed at runtime by the call-graph of topologically-nested functions.



Calls the provided expression with an Id specific to the callsite, optionally passing additional environment values to the child scope.


todo document

Attribute Macros


Transforms a function declaration into a topologically-nested function which, when called, attaches its call subtopology to that of its caller's (parent's).