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I Wrote Go-TinyDate, The Missing Golang Date Package

wagslane profile image Lane Wagner Originally published at qvault.io on ・3 min read

time.Time makes dealing with dates and times in Go a breeze, and it even comes bundled in the standard library! However, a time.Time{} struct uses more than 24 bytes of memory under most conditions, and I’ve run into situations where I need to store millions of them in memory, but all I really needed was a UTC date! Go-TinyDate solves this with just 4 bytes of memory.

Star the Github! https://github.com/lane-c-wagner/go-tinydate

How?

Let’s look at the time.Time struct:

type Time struct {
    wall uint64 // 8 bytes
    ext int64 // b bytes
    loc *Location // 8 bytes if not nil, plus location memory
}

type Location struct {
    name string // unlimited
    zone []zone // unlimited
    tx []zoneTrans // unlimited
    cacheStart int64 // 8 bytes
    cacheEnd int64 // 8 bytes
    cacheZone *zone // 8 bytes if not nil, plus zone
}

type zone struct {
    name string // unlimited
    offset int // 4-8 bytes depending on OS
    isDST bool // 1 bit
}

type zoneTrans struct {
    when int64 // 8 bytes
    index uint8 // 1 byte
    isstd, isutc bool // 1 bit
}

https://golang.org/src/time/time.go?s=6278:7279#L117

As you can see, depending on how the TimeZone is set, there can be quite a bit of memory allocated just to store a time.Time. Even if there is no location set, the lower-bound is still 16 bytes.

Contrast with a tinydate.TinyDate{}:

type TinyDate struct {
    year uint16 // 2 byte
    month uint8 // 1 byte
    day uint8 // 1 byte
}

Only 4 bytes! We give up the ability to track anything more specific than the date, but often that is all we need.

Quick Start

Create a date and add to it:

package main

import (
    tinydate "github.com/lane-c-wagner/go-tinydate"
)

func main(){
    td, err := tinydate.New(2020, 04, 3)
    if err != nil {
        fmt.Println(err.Error())
    }

    td = td.Add(time.Hour * 48)
    fmt.Println(td)
    // prints 2020-04-05
}

Or Cast a time to a tinydate and back:

newTinydate, err := FromTime(time.Now())
if err != nil{
    fmt.Println(err.Error())
}
convertedTime := newTinydate.ToTime()

When Should I Use It?

As the TinyDate Readme states, if you aren’t constrained for resources, better to stick with the standard time.Time. But the following situations can be good reasons to switch to TinyDate:

  • You are working in embedded systems and every byte counts
  • You are working on a system that stores thousands of dates, and reducing memory costs by >75% is significant
  • You are sure you will never need more than date precision

Why No Timezones?

The main reason? Timezones are the most memory heavy part of a time.Time struct, yet the best practice is usually to store dates and times only in UTC. TinyDate stays tiny by always storing dates in UTC, but still gives the ability to calculate dates in other timezones via methods like ParseInLocation FromTime and ToTime.

API

The tinydate.Tinydate API largely mirrors that of time.Time. The only methods missing are the ones that make no sense without timezone or intra-day support. Check out the godoc for reference: https://godoc.org/github.com/lane-c-wagner/go-tinydate

Thanks For Reading

Hit me up on twitter @wagslane if you have any questions or comments.

Lane on Dev.to: wagslane

If you like the package, give it a Star on Github

The post I Wrote Go-TinyDate, The Missing Golang Date Package appeared first on Qvault.

Discussion

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Tudor Hulban

What would be the advantage over using a struct with just UNIX time?

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Lane Wagner Author

That's a good point - For the same memory (uint32) you could get second precision, but you give up being able to represent quite as many dates.

Edit: Also, using day, month, year supports from year 0 to year 65535. Unix time supports from 1970 to ~2100

Maybe I'll make a go-tinytime package that does what you suggest. It essentially gets second precision at the cost of fewer date options.

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