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proposal: time: export time.isLeap #20944

petrus-v opened this issue Jul 7, 2017 · 3 comments

proposal: time: export time.isLeap #20944

petrus-v opened this issue Jul 7, 2017 · 3 comments


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@petrus-v petrus-v commented Jul 7, 2017

What version of Go are you using (go version)?


What operating system and processor architecture are you using (go env)?

linux / amd64

What did you do?

package main

import (

func main() {
	fmt.Println("Hello, playground", time.isLeap(2000))

I'm pretty new with golang, I wanted to progress and start some exercises from!

the idea was to use the isLeap method from time pacakge, as far I understand function starting with low letter are not exported (public) and visible from other packages. Am I wrong?

In this huge repo, is there some rules to choose if a method should be exported or not?

What did you expect to see?

I'd like to avoid duplicate isLeap method as long Go SDK could provide it for me!

expected output

Hello, playground true

What did you see instead?

tmp/sandbox140448971/main.go:9: cannot refer to unexported name time.isLeap
tmp/sandbox140448971/main.go:9: undefined: time.isLeap

As I'm new here, I hope I haven't miss something evident! I guess this issue can be a bit controversial or subjective please close it if too many people speak (loose time) about it!

I through it's a good start to learn the contributing flow, so if some people are Ok with this proposal I would be please to follow the contributing Guide!

@ALTree ALTree changed the title Proposal to export time.isLeap func proposal: time: export time.isLeap Jul 7, 2017
@gopherbot gopherbot added this to the Proposal milestone Jul 7, 2017
@gopherbot gopherbot added the Proposal label Jul 7, 2017
@ALTree ALTree modified the milestones: Go1.10, Proposal Jul 7, 2017
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@ALTree ALTree commented Jul 7, 2017

Am I wrong?

You are correct: the function is there but it's not exported:

func isLeap(year int) bool {
	return year%4 == 0 && (year%100 != 0 || year%400 == 0)

I'm not sure it would be worth it to make the time API bigger (it is already quite big) for a function this simple to write.

I've tagged this as a proposal, leaving for others to decide.

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@bradfitz bradfitz commented Jul 7, 2017

There's a cost (maintenance, documentation, cognitive load from doc/API bloat) to exporting unnecessary or uncommon things.

The proposal process and gathering the data to justify why this should be exported and showing how many people would benefit will be more work than just doing the exercism exercise.

I doubt many people would need IsLeap.

You can just copy it (as @ALTree showed above). Even if you didn't know the leap year rules, you could use the time package to extract the information too:

func IsLeap(year int) bool {
	lastDayFeb := time.Date(year, time.February, 28, 0, 0, 0, 0, time.UTC)
	nextDay := lastDayFeb.AddDate(0, 0, 1)
	return nextDay.Month() == time.February

(but that's less efficient than just year%4 == 0 && (year%100 != 0 || year%400 == 0))

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@petrus-v petrus-v commented Jul 8, 2017

Thanks for replies, I get your point.

And it's true I've probably used less than 10 times isLeap method on professional projects for at least 10 years in other languages. So we are letting that cost to projects that require isLeap function, I'm closing this issue!

@petrus-v petrus-v closed this Jul 8, 2017
@golang golang locked and limited conversation to collaborators Jul 8, 2018
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