// Suppose you manage a fleet of servers that have various services running
// on them, and you want to statically allocate a user id for a system user
// for each of these services. We could define a mapping of service name to
// uid like so:
let uids = {
  goat-teleporter = 10_000,
  logs-archiver = 10_001,
  device-monitor = 10_002,
  prometheus-node-exporter = 10_003,

  // Uncomment the following line to trigger the problem explained below.
  // prometheus-smartctl-exporter = 10_003,
};

// However, in this configuration it is easy to accidentally use the same uid
// twice, which would be disastrous. We can prevent this statically by inverting
// the mapping, and using `key_by`.
let all_users = [for name, uid in uids: { name = name, uid = uid }];
let users_by_uid = all_users.key_by(u => u.uid);

uids