Fast strftime in Go with BCP 47 language tags.

It is either possible to instanciate an object for a given locale (via strftime.New) or directly call strftime.Format or strftime.EnFormat.

To simply get a timestamp in English:

fmt.Printf("%s: something happened", strftime.EnFormat(`%c`, time.Now()));

Or get a quick result in French:

fmt.Printf("%s: Quelque chose est arrivé", strftime.Format(language.French, `%c`, time.Now()));

Or display a result in the appropriate language for a web user:

tags, _, _ := language.ParseAcceptLanguage(r.Header.Get("Accept-Language"))
f := strftime.New(tags...)
f.FormatF(w, `%c`, time.Now());

This version of strftime for Go has multiple goals in mind:

• Support for BCP 47 language tags
• Easy to use
• Ability to just return string or write to a io.Writer
• Be as complete as possible in terms of conversion specifications

Era modifiers are available. For locales in which there is no era, normal values (without era modifier) are returned.

This is a very good question. Go time package's Format() method has a nice, human friendly method to set the format for a date. Yet, this is unfortunately not appropriate when multiple languages are involved, as each language has its own rules in terms of terms ordering and presentation, and may even use different years.

While maybe less human friendly, strftime() has a long history and most developers will know how it works and what to expect from it.

// On Linux Gentoo 4.14.13-gentoo
// go version go1.11 linux/amd64
$ go test -tags bench -benchmem -bench .
<snip>
BenchmarkCactus-12        	 1000000	      1697 ns/op	     216 B/op	       7 allocs/op
BenchmarkLeekchan-12      	  500000	      2775 ns/op	    1376 B/op	      22 allocs/op
BenchmarkTebeka-12        	  500000	      3777 ns/op	     288 B/op	      21 allocs/op
BenchmarkJehiah-12        	 1000000	      1555 ns/op	     256 B/op	      17 allocs/op
BenchmarkFastly-12        	  500000	      3774 ns/op	     192 B/op	      11 allocs/op
BenchmarkLestrrat-12      	 1000000	      1333 ns/op	     240 B/op	       3 allocs/op
BenchmarkKarpelesLab-12    	 2000000	       688 ns/op	     240 B/op	       3 allocs/op
PASS
ok  	github.com/KarpelesLab/strftime	11.997s

This library is much faster than other libraries for common cases. In case of format pattern re-use, Lestrrat's implementation is still faster (but has no locale awareness).

Please note that this benchmark only uses the subset of conversion specifications that are supported by ALL of the libraries compared.