Function imm_code_to_dates 

pub fn imm_code_to_dates(
    code: &str,
    cycle: ImmCycle,
) -> Result<(NaiveDate, NaiveDate), ImmCodeError>

Resolves an IMM code (three-letter month + two-digit year, e.g. "JUN27") to its unadjusted (start, end) reference-period dates: the period of the futures contract the code names, as a FutureTemplate’s reference period read it.

start is the third Wednesday of the named month-year; end is the third Wednesday of the next IMM in cycle (3 months later for ImmCycle::Imm3M, 1 month later for ImmCycle::Imm1M). Years resolve in the 2000–2099 window. A CME month letter and year ("H22") names the same month as "MAR22". A quarterly code naming a non-cycle month (e.g. "JAN27"), or any code outside the MMM + YY and letter + YY shapes, is rejected.

Errors

ImmCodeError carrying code when it is not five bytes, does not split cleanly into a three-letter month and a two-digit year, names no month in the table, or — under ImmCycle::Imm3M — names a month outside the quarterly cycle.