time.daysIn(month, year)

[Peregrinati]

Is there a reason time.daysIn(month, year) is not exported? Just now I wanted such a function and went to time.go looking for inspiration. Lo and behold, there it is, but it's inaccessible.

[peterGo]

Peregrinati,

Since the time.daysIn(month, year) function is not exported, you have
to write your own function. To avoid replicating the
time.daysIn(month, year) logic and data, I write:

package main

import (
"fmt"
"time"
)

// daysIn returns the number of days in a month for a given year.
func daysIn(m time.Month, year int) int {
// This is equivalent to time.daysIn(m, year).
return time.Date(year, m+1, 0, 0, 0, 0, 0, time.UTC).Day()
}

func main() {
fmt.Println(daysIn(1, 2000))
fmt.Println(daysIn(2, 2000))
fmt.Println(daysIn(2, 2001))
fmt.Println(daysIn(6, 2000))
fmt.Println(daysIn(12, 2000))
}

/*
Output:
31
29
28
30
31
*/

Peter

[Ben Barbour]

Hi Peter,

Thanks for the function. I already wrote my own, but yours looks simpler.

What I was asking wasn't how to implement it though... I am curious if there's a reason the function isn't exported that I'm just not seeing. Did the developers just think nobody would need it given how simple it is to write your own with Date()?

[Kyle Lemons]

The more compelling reason is probably to keep the exported API simple.  The more functions that are exported that are helperish in nature, the harder it is to comprehend the entire API.  As it is, it's not that hard to know pretty much the entire standard library.  Perhaps a time/timeutil could be added with such helpers, but I don't think they would fit in time.

[si guy]

I have a continuous appreciation of this philosophy, it is a _massive_ time-saver.

[pa...@daishisystems.com]

You can leverage https://github.com/daishisystems/month to achieve this.

[Matt Harden]

It's trivial to implement in terms of the Time package. http://play.golang.org/p/H2cx1PLQRd

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[peterGo]

Matt,

From my earlier answer, it's simpler than that: https://groups.google.com/d/msg/Golang-nuts/W-ezk71hioo/6qRWMupJoMYJ

http://play.golang.org/p/TcIX8kWQRW

Peter

[Peter Kleiweg]

I can see why this would not be exported.

Feeding an invalid date to get
something useful, that might brake when the implementation of Date changes.

Saver would be to feed a valid date, with first of the month, then add one month, then subtract one day.

Or simply use the know rules for number of days in a month. They are not difficult.

[Matt Harden]

The documentation of Date specifically describes how invalid dates are normalized. This won't break when the implementation of Date changes.

[Ben Barbour]

Ah, that's the kind of answer I was looking for, thanks Peter.