Function topo::call

pub fn call<F, R>(op: F) -> R where
    F: FnOnce() -> R, 

Calls the provided function as a child of CallId::current, using for a slot the number of times the given source location has been called during the current parent’s scope.

This is a useful default for calls which are not expected to repeat at the same callsite during the parent scope, i.e. those that will only be called once per scope. It is also a useful default for calls that will occur in a loop where the positional index is the primary way of identifying repeated entries into the child scope.

See CallId, root, call_in_slot, and nested.

Example

use topo::{call, root, CallId};

let get_list_of_ids = || {
    topo::call(|| {
        let mut ids = vec![];
        for i in 0..3 {
            let current = call(CallId::current);
            if i > 0 {
                assert_ne!(ids[i - 1], current, "each CallId is different from the last");
            }
            ids.push(current);
        }
        ids
    })
};

// without a parent call, each of these behaves as its own root
assert_eq!(get_list_of_ids(), get_list_of_ids());

// ...and explicitly wrapping each call in a root(...) produces the same result
assert_eq!(root(get_list_of_ids), root(get_list_of_ids), "explicit roots match");

// but when they're siblings under a single call, they produce distinct results
call(|| assert_ne!(get_list_of_ids(), get_list_of_ids(), "siblings don't match"));