Function week_of 

pub fn week_of(
    calendar: &WeekCalculator,
    num_days_in_previous_unit: u16,
    num_days_in_unit: u16,
    day: u16,
    week_day: IsoWeekday,
) -> Result<WeekOf, CalendarError>

Computes & returns the week of given month/year according to calendar.

Arguments

• calendar: Calendar information used to compute the week number.
• num_days_in_previous_unit: The number of days in the preceding month/year.
• num_days_in_unit: The number of days in the month/year.
• day: 1-based day of month/year.
• week_day: The weekday of day..