A time matches an expression only if each of its fields is an allowed value. Today you build the matcher for the three straightforward fields - minute, hour, and month - leaving the tangled day fields for next.
Return whether a timestamp's minute, hour, and month are each members of the expression's corresponding sets.
A cron expression matches an instant when every field of the expression allows that instant’s corresponding value. Three of the five fields are completely independent and combine with a plain AND: the minute must be in the minute set, the hour in the hour set, and the month in the month set. Because each field is already a set of allowed values, matching one field is a single membership test, and the whole thing is those tests joined with AND.
Leave the two day fields out of Matches for now - treat any day as acceptable this
lesson - because they do not combine so simply. 30 9 * 1 * fires at 09:30 in
January regardless of the day, so it matches 2024-01-15 09:30 but not 09:31 (wrong
minute) and not a June instant (wrong month). Getting the three easy fields locked
down first means the next lessons can focus entirely on the day-of-month and
day-of-week rule without anything else in the way.
func Matches(e Expr, t time.Time) bool {minute, hour, _, month, _ := timeFields(t)return e.Minute[minute] && e.Hour[hour] && e.Month[month]// day-of-month and day-of-week join in the next lessons.}