Function i64_of 

fn i64_of(y: &Yaml) -> i64

A 64-bit integer out of a response, whichever way it was encoded.

The API renders an int64 as a JSON string (section 7.6) — from, to, avg_nano — because 1.7e18 does not survive a double, and a counter small enough to be safe is rendered as a number. Both shapes reach here.