go-strftime

strftime for Go

WARNING

This repository has been moved to github.com/lestrrat-go/strftime. This repository exists so that libraries pointing to this URL will keep functioning, but this repository will NOT be updated in the future. Please use the new import path.

SYNOPSIS

f := strftime.New(`.... pattern ...`)
if err := f.Format(buf, time.Now()); err != nil {
    log.Println(err.Error())
}

DESCRIPTION

The goals for this library are

• Optimized for the same pattern being called repeatedly
• Be flexible about destination to write the results out
• Be as complete as possible in terms of conversion specifications

API

Format(string, time.Time) (string, error)

Takes the pattern and the time, and formats it. This function is a utility function that recompiles the pattern every time the function is called. If you know beforehand that you will be formatting the same pattern multiple times, consider using New to create a Strftime object and reuse it.

New(string) (*Strftime, error)

Takes the pattern and creates a new Strftime object.

obj.Pattern() string

Returns the pattern string used to create this Strftime object

obj.Format(io.Writer, time.Time) error

Formats the time according to the pre-compiled pattern, and writes the result to the specified io.Writer

obj.FormatString(time.Time) string

Formats the time according to the pre-compiled pattern, and returns the result string.

SUPPORTED CONVERSION SPECIFICATIONS

pattern	description
%A	national representation of the full weekday name
%a	national representation of the abbreviated weekday
%B	national representation of the full month name
%b	national representation of the abbreviated month name
%C	(year / 100) as decimal number; single digits are preceded by a zero
%c	national representation of time and date
%D	equivalent to %m/%d/%y
%d	day of the month as a decimal number (01-31)
%e	the day of the month as a decimal number (1-31); single digits are preceded by a blank
%F	equivalent to %Y-%m-%d
%H	the hour (24-hour clock) as a decimal number (00-23)
%h	same as %b
%I	the hour (12-hour clock) as a decimal number (01-12)
%j	the day of the year as a decimal number (001-366)
%k	the hour (24-hour clock) as a decimal number (0-23); single digits are preceded by a blank
%l	the hour (12-hour clock) as a decimal number (1-12); single digits are preceded by a blank
%M	the minute as a decimal number (00-59)
%m	the month as a decimal number (01-12)
%n	a newline
%p	national representation of either "ante meridiem" (a.m.) or "post meridiem" (p.m.) as appropriate.
%R	equivalent to %H:%M
%r	equivalent to %I:%M:%S %p
%S	the second as a decimal number (00-60)
%T	equivalent to %H:%M:%S
%t	a tab
%U	the week number of the year (Sunday as the first day of the week) as a decimal number (00-53)
%u	the weekday (Monday as the first day of the week) as a decimal number (1-7)
%V	the week number of the year (Monday as the first day of the week) as a decimal number (01-53)
%v	equivalent to %e-%b-%Y
%W	the week number of the year (Monday as the first day of the week) as a decimal number (00-53)
%w	the weekday (Sunday as the first day of the week) as a decimal number (0-6)
%X	national representation of the time
%x	national representation of the date
%Y	the year with century as a decimal number
%y	the year without century as a decimal number (00-99)
%Z	the time zone name
%z	the time zone offset from UTC
%%	a '%'

PERFORMANCE / OTHER LIBRARIES

The following benchmarks were run separately because some libraries were using cgo on specific platforms (notabley, the fastly version)

// On my OS X 10.11.6, 2.9 GHz Intel Core i5, 16GB memory.
// go version go1.8rc1 darwin/amd64
hummingbird% go test -tags bench -benchmem -bench .
<snip>
BenchmarkTebeka-4                     300000          4469 ns/op         288 B/op         21 allocs/op
BenchmarkJehiah-4                    1000000          1931 ns/op         256 B/op         17 allocs/op
BenchmarkFastly-4                    2000000           724 ns/op          80 B/op          5 allocs/op
BenchmarkLestrrat-4                  1000000          1572 ns/op         240 B/op          3 allocs/op
BenchmarkLestrratCachedString-4      3000000           548 ns/op         128 B/op          2 allocs/op
BenchmarkLestrratCachedWriter-4       500000          2519 ns/op         192 B/op          3 allocs/op
PASS
ok      github.com/lestrrat/go-strftime 22.900s

// On a host on Google Cloud Platform, machine-type: n1-standard-4 (vCPU x 4, memory: 15GB)
// Linux <snip> 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/Linux
// go version go1.8rc1 linux/amd64
hummingbird% go test -tags bench -benchmem -bench .
<snip>
BenchmarkTebeka-4                     500000          3904 ns/op         288 B/op         21 allocs/op
BenchmarkJehiah-4                    1000000          1665 ns/op         256 B/op         17 allocs/op
BenchmarkFastly-4                    1000000          2134 ns/op         192 B/op         13 allocs/op
BenchmarkLestrrat-4                  1000000          1327 ns/op         240 B/op          3 allocs/op
BenchmarkLestrratCachedString-4      3000000           498 ns/op         128 B/op          2 allocs/op
BenchmarkLestrratCachedWriter-4      1000000          3390 ns/op         192 B/op          3 allocs/op
PASS
ok      github.com/lestrrat/go-strftime 44.854s

This library is much faster than other libraries IF you can reuse the format pattern.

Here's the annotated list from the benchmark results. You can clearly see that (re)using a Strftime object and producing a string is the fastest. Writing to an io.Writer seems a bit sluggish, but since the one producing the string is doing almost exactly the same thing, we believe this is purely the overhead of writing to an io.Writer

Import Path	Score	Note
github.com/lestrrat/go-strftime	3000000	Using FormatString() (cached)
github.com/fastly/go-utils/strftime	2000000	Pure go version on OS X
github.com/lestrrat/go-strftime	1000000	Using Format() (NOT cached)
github.com/jehiah/go-strftime	1000000
github.com/fastly/go-utils/strftime	1000000	cgo version on Linux
github.com/lestrrat/go-strftime	500000	Using Format() (cached)
github.com/tebeka/strftime	300000

However, depending on your pattern, this speed may vary. If you find a particular pattern that seems sluggish, please send in patches or tests.

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

Somethings to consider when making performance comparisons in the future:

• Can it write to io.Writer?
• Which %specification does it handle?