Function run_id 

pub fn run_id(task: &str, variant: &str, repetition: u32) -> String

The id of a run: task, variant, repetition. One file per id; a recorded run is never overwritten.

use majordomus_cli::economics::runner::run_id;
let id = run_id("storage-v2", "majordomus", 1);
assert_eq!(id, "storage-v2--majordomus--r1");
// the two arms of one task and repetition differ in the variant alone
assert_ne!(run_id("storage-v2", "baseline", 1), id);