Convert camel case to snake case in Go http://play.golang.org/p/9ybqJat1Hr

ToSnakeCase.go

import (
	"fmt"
	"strings"
	"regexp"
)

var matchFirstCap = regexp.MustCompile("(.)([A-Z][a-z]+)")
var matchAllCap   = regexp.MustCompile("([a-z0-9])([A-Z])")

func ToSnakeCase(str string) string {
	snake := matchFirstCap.ReplaceAllString(str, "${1}_${2}")
	snake  = matchAllCap.ReplaceAllString(snake, "${1}_${2}")
	return strings.ToLower(snake)
}

@porfirion thanks for the proposal and comparison! I noticed most of my unit test fail when using your version. Therefore, I tried to make a version which succeeds (nearly) all tests. It can still use some cleanup and unit test for HTTPRequest still fails, but nearly same performance improvements.

Code

func ToSnakeCase(s string) string {
	var res = make([]rune, 0, len(s))
	var p = '_'
	for i, r := range s {
		if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
			res = append(res, '_')
		} else if unicode.IsUpper(r) && i > 0 {
			if unicode.IsLetter(p) && !unicode.IsUpper(p) || unicode.IsDigit(p) {
				res = append(res, '_', unicode.ToLower(r))
			} else {
				res = append(res, unicode.ToLower(r))
			}
		} else {
			res = append(res, unicode.ToLower(r))
		}

		p = r
	}
	return string(res)
}

Benchmarks

func BenchmarkToSnakeCaseRegex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		ToSnakeCaseRegex("BatteryLifeValue")
	}
}

func BenchmarkToSnakeCase(b *testing.B) {
	for i := 0; i < b.N; i++ {
		ToSnakeCase("BatteryLifeValue")
	}
}

Results

BenchmarkToSnakeCaseRegex-12    	  360540	      3282 ns/op	     282 B/op	      11 allocs/op
BenchmarkToSnakeCase-12         	 1726478	       714 ns/op	     224 B/op	       3 allocs/op

@JensSkipr @porfirion

Hi, I make one more, but it pass all test, and better performance.

source file in here: https://gist.github.com/hxsf/7f5392c0153d3a8607c42eefed02b8cd

Bench

> go test -benchmem -bench 'One'
goos: darwin
goarch: amd64
pkg: mesh-sidecar/cmd/vars
cpu: Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
BenchmarkOneCase/ToSnakeCaseRegex-8               490156              2403 ns/op             305 B/op         12 allocs/op
BenchmarkOneCase/ToSnakeCaseByJensSkipr-8        4163742               286.1 ns/op           216 B/op          3 allocs/op
BenchmarkOneCase/ToSnakeCase-8                   8867581               131.4 ns/op            24 B/op          1 allocs/op

BenchmarkAllInOne/ToSnakeCaseRegex-8               51538             22480 ns/op            2307 B/op        137 allocs/op
BenchmarkAllInOne/ToSnakeCaseByJensSkipr-8        395026              3051 ns/op            1352 B/op         41 allocs/op
BenchmarkAllInOne/ToSnakeCase-8                   857940              1491 ns/op             232 B/op         17 allocs/op
PASS
ok      mesh-sidecar/cmd/vars   7.930s

@hxsf looks awesome! Yeah, I forgot about additional capacity for underscores %)

@hxsf: That looks great! Do you mind adding a license to your gist?

@adombeck add MIT license.

@hxsf: Great, thanks a lot!

@hxsf Test failed for

MyLIFEIsAwesomE should be my_life_is_awesom_e but got mylife_is_awesome
Japan125Canada130Australia150 should be japan125_canada130_australia150 but got japan1_2_5_canada1_3_0_australia1_5_0

@elvizlai I update the code. and it works

good guys ! keep it up!
kebab case should be concluded here as well

@abdennour just replace '_' with '-' in the code, and change the function name. I think it will work.