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// Package Clock is a small library for keeping track of time.
package clock
import "fmt"
// Clock type
type Clock int
const (
dayMinutes = 1440
hourMinutes = 60
)
func normalize(minutes int) Clock {
if minutes < 0 {
return Clock(dayMinutes + (minutes % dayMinutes))
} else if minutes >= dayMinutes {
return Clock(minutes % dayMinutes)
}
return Clock(minutes)
}
// New returns a Clock that represents the hour and minutes.
func New(hour, minutes int) Clock {
return normalize(hour*hourMinutes + minutes)
}
// Add returns a Clock that represents the Clock plus minutes.
func (clock Clock) Add(minutes int) Clock {
return normalize(int(clock) + minutes)
}
// Subtract returns a Clock that represents the Clock minus minutes.
func (clock Clock) Subtract(minutes int) Clock {
return normalize(int(clock) - minutes)
}
// String returns the Clock formatted into hours:minutes, e.g. 01:02.
func (clock Clock) String() string {
return fmt.Sprintf("%02d:%02d", clock/hourMinutes, clock%hourMinutes)
}
The approach imports the fmt package so it can use the fmt.Sprintf() function in the String() method.
This approach starts by typing Clock as an int.
It then defines a couple of constants with meaningful names for 1440 and 60,
instead of using the literals as magic numbers.
The normalize() helper function is defined to properly handle rollover for when adding or subtracting minutes crosses into the next or previous day(s).
There are other ways to handle rollover, such as the following expression:
((hours*hourMinutes+minutes)%dayminutes + dayMinutes) % dayMinutes
Since normalize() returns a Clock, it can be used by the New function as well as the Add and Subtract methods.
Note that, in the Add and Subtractmethods, the received Clock argument must be converted to an int to be
added to or subtracted by the int minutes, even though the underlying type of Clock is an int.
This can be helpful if two int values are two different types, such as a meter and a foot.
The compiler will not allow adding a meter type to a foot type,
even if both are an int, unless one of them is converted to the other.
For an example of why this is important, see an article on how a $125 million spacecraft crashed because of a
mix-up between English and metric units of measure.
The String() function uses fmt.Sprintf() to format the hour and minutes with leading zeros.
If the amount of minutes is 69, then the hour is 69 divided by 60 (1),
and the minutes is the remainder of 69 divided by 60 (9), so the string for 69 minutes would be 01:09.
The format specifier %02d says to pad a base-10 number with zeros for up to two places.
If one place is occupied by a digit, then the extra place is padded with a zero.
More info can be found at a format cheat sheet.
