Limitations of Go date format logic

Software

Go’s date formats are a special beast, as everyone else already realised a decade ago. I’m not a Go developer, but I do use a few devops and blogging tools written in it, and as such I work regularly with its unconventional date representation.

Unlike other languages, Go works against a reference date which you refactor to get the format you’re after:

Mon Jan 2 15:04:05 -0700 MST 2006

I can see the appeal of this rather than an alphabet soup like strftime, even though I committed most of that to memory by now. It’s more WYSIWYG, and easier to visualise in something like a template.

I always wanted to know why this specific date, for reasons I’ll get to in a moment. It lead me to this old Hacker News thread from 2015, and a quote from the documentation that shows this ascending mnemonic:

Mon Jan 2 15:04:05 -0700 MST 2006
0   1   2  3  4  5              6

But there are some assumptions and i17n drawbacks here. Non-American readers would have immediately spotted a problem: we generally don’t put months first. Most of us would write long dates like this:

Mon 2 Jan 15:04:05 -0700 MST 2006
0   2 1    3  4  5              6

It’s not a big deal, the mnemonic holds even though it doesn’t have the elegant ascending numbers anymore. But it’s a bit weird.

The far bigger problem comes when you want to validate short dates. Americans use MM-DD-YYYY, whereas the rest of us use DD-MM-YYYY. At a glance, will this render as the first of February, or the second of January?

02-01-2021

Using a day (02) and a month (01) that can be easily confused is, to use the Shakespearean term, a huge pain in the asp. I can’t tell you how many times I’ve looked at a template and had to do a double-take on the date, or troubleshooting why the months on a page are all wrong.

Conventional wisdom in documentation is to always use a day greater than 12 to remove global ambiguity. The order of this date looks wrong to me, but at least it’s mutually intelligible:

01-27-2021

We’d all be using YYYY-MM-DD in an ideal world, but alas we’re all stuck in meatspace. I’ll continue to work around this, but it’s disappointing that such a high-profile tool would make this difficult to satisfy a mnemonic that doesn’t even hold that well outside the US.

Author bio and support

Me!

Ruben Schade is a technical writer and IaaS engineer in Sydney, Australia who refers to himself in the third person in bios. Wait, not BIOS… my brain should be EFI by now.

The site is powered by Hugo, FreeBSD, and OpenZFS on OrionVM, everyone’s favourite cloud infrastructure provider.

If you found this post helpful or entertaining, you can shout me a coffee or buy some silly merch. Thanks!