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Go Strcase

Go Report Card Coverage GoDoc

Convert strings to snake_case, camelCase, PascalCase, kebab-case and more! Supports Go initialisms, customization, and Unicode.

import "github.com/ettle/strcase"

Overview

Package strcase is a package for converting strings into various word cases (e.g. snake_case, camelCase)

go get -u github.com/ettle/strcase

Example usage

strcase.ToSnake("Hello World")     // hello_world
strcase.ToSNAKE("Hello World")     // HELLO_WORLD

strcase.ToKebab("helloWorld")      // hello-world
strcase.ToKEBAB("helloWorld")      // HELLO-WORLD

strcase.ToPascal("hello-world")    // HelloWorld
strcase.ToCamel("hello-world")     // helloWorld

// Handle odd cases
strcase.ToSnake("FOOBar")          // foo_bar

// Support Go initialisms
strcase.ToGoCamel("http_response") // HTTPResponse

// Specify case and delimiter
strcase.ToCase("HelloWorld", strcase.UpperCase, '.') // HELLO.WORLD

Why this package

String strcase is pretty straight forward and there are a number of methods to do it. This package is fully featured, more customizable, better tested, and faster* than other packages and what you would probably whip up yourself.

Unicode support

We work for with unicode strings and pay very little performance penalty for it as we optimized for the common use case of ASCII only strings.

Customization

You can create a custom caser that changes the behavior to what you want. This customization also reduces the pressure for us to change the default behavior which means that things are more stable for everyone involved. The goal is to make the common path easy and fast, while making the uncommon path possible.

 c := NewCaser(
	// Use Go's default initialisms e.g. ID, HTML
 	true,
	// Override initialisms (e.g. don't initialize HTML but initialize SSL
 	map[string]bool{"SSL": true, "HTML": false},
	// Write your own custom SplitFn
	//
 	NewSplitFn(
 		[]rune{'*', '.', ','},
 		SplitCase,
 		SplitAcronym,
 		PreserveNumberFormatting,
 		SplitBeforeNumber,
 		SplitAfterNumber,
 	))
 assert.Equal(t, "http_200", c.ToSnake("http200"))

Initialism support

By default, we use the golint intialisms list. You can customize and override the initialisms if you wish to add additional ones, such as "SSL" or "CMS" or domain specific ones to your industry.

ToGoCamel("http_response") // HTTPResponse
ToGoSnake("http_response") // HTTP_response

Test coverage

We have a wide ranging test suite to make sure that we understand our behavior. Test coverage isn't everything, but we aim for 100% coverage.

Fast

Optimized to reduce memory allocations with Builder. Benchmarked and optimized around common cases.

We're on par with the fastest packages (that have less features) and much faster than others. We also benchmarked against code snippets. Using string builders to reduce memory allocation and reordering boolean checks for the common cases have a large performance impact.

Hopefully I was fair to each library and happy to rerun benchmarks differently or reword my commentary based on suggestions or updates.

// This package
// Go intialisms and custom casers are slower
BenchmarkToTitle-4                992491              1559 ns/op              32 B/op          1 allocs/op
BenchmarkToSnake-4               1000000              1475 ns/op              32 B/op          1 allocs/op
BenchmarkToSNAKE-4               1000000              1609 ns/op              32 B/op          1 allocs/op
BenchmarkToGoSnake-4              275010              3697 ns/op              44 B/op          4 allocs/op
BenchmarkToCustomCaser-4          342704              4191 ns/op              56 B/op          4 allocs/op

// Segment has very fast snake case and camel case libraries
// No features or customization, but very very fast
BenchmarkSegment-4               1303809               938 ns/op              16 B/op          1 allocs/op

// Stdlib strings.Title for comparison, even though it only splits on spaces
BenchmarkToTitleStrings-4        1213467              1164 ns/op              16 B/op          1 allocs/op

// Other libraries or code snippets
// - Most are slower, by up to an order of magnitude
// - None support initialisms or customization
// - Some generate only camelCase or snake_case
// - Many lack unicode support
BenchmarkToSnakeStoewer-4         973200              2075 ns/op              64 B/op          2 allocs/op
// Copying small rune arrays is slow
BenchmarkToSnakeSiongui-4         264315              4229 ns/op              48 B/op         10 allocs/op
BenchmarkGoValidator-4            206811              5152 ns/op             184 B/op          9 allocs/op
// String alloction is slow
BenchmarkToSnakeFatih-4            82675             12280 ns/op             392 B/op         26 allocs/op
BenchmarkToSnakeIanColeman-4       83276             13903 ns/op             145 B/op         13 allocs/op
// Regexp is slow
BenchmarkToSnakeGolangPrograms-4   74448             18586 ns/op             176 B/op         11 allocs/op

// These results aren't a surprise - my initial version of this library was
// painfully slow. I think most of us, without spending some time with
// profilers and benchmarks, would write also something on the slower side.

Why not this package

If every nanosecond matters and this is used in a tight loop, use segment.io's libraries (https://github.com/segmentio/go-snakecase and https://github.com/segmentio/go-camelcase). They lack features, but make up for it by being blazing fast. Alternatively, if you need your code to work slightly differently, fork them and tailor it for your use case.

If you don't like having external imports, I get it. This package only imports packages for testing, otherwise it only uses the standard library. If that's not enough, you can use this repo as the foundation for your own. MIT Licensed.

This package is still relatively new and while I've used it for a while personally, it doesn't have the miles that other packages do. I've tested this code agains't their test cases to make sure that there aren't any surprises.

Migrating from other packages

If you are migrating from from another package, you may find slight differences in output. To reduce the delta, you may find it helpful to use the following custom casers to mimic the behavior of the other package.

// From <a href="https://github.com/iancoleman/strcase">https://github.com/iancoleman/strcase</a>
var c = NewCaser(false, nil, NewSplitFn([]rune{'_', '-', '.'}, SplitCase, SplitAcronym, SplitBeforeNumber))

// From <a href="https://github.com/stoewer/go-strcase">https://github.com/stoewer/go-strcase</a>
var c = NewCaser(false, nil, NewSplitFn([]rune{'_', '-'}, SplitCase), SplitAcronym)

Index

func ToCamel

func ToCamel(s string) string

ToCamel returns words in camelCase (capitalized words concatenated together, with first word lower case). Also known as lowerCamelCase or mixedCase.

func ToCase

func ToCase(s string, wordCase WordCase, delimiter rune) string

ToCase returns words in given case and delimiter.

func ToGoCamel

func ToGoCamel(s string) string

ToGoCamel returns words in camelCase (capitalized words concatenated together, with first word lower case). Also known as lowerCamelCase or mixedCase.

Respects Go's common initialisms (e.g. httpResponse -> HTTPResponse).

func ToGoCase

func ToGoCase(s string, wordCase WordCase, delimiter rune) string

ToGoCase returns words in given case and delimiter.

Respects Go's common initialisms (e.g. httpResponse -> HTTPResponse).

func ToGoKebab

func ToGoKebab(s string) string

ToGoKebab returns words in kebab-case (lower case words with dashes). Also known as dash-case.

Respects Go's common initialisms (e.g. http-response -> HTTP-response).

func ToGoPascal

func ToGoPascal(s string) string

ToGoPascal returns words in PascalCase (capitalized words concatenated together). Also known as UpperPascalCase.

Respects Go's common initialisms (e.g. HttpResponse -> HTTPResponse).

func ToGoSnake

func ToGoSnake(s string) string

ToGoSnake returns words in snake_case (lower case words with underscores).

Respects Go's common initialisms (e.g. http_response -> HTTP_response).

func ToKEBAB

func ToKEBAB(s string) string

ToKEBAB returns words in KEBAB-CASE (upper case words with dashes). Also known as SCREAMING-KEBAB-CASE or SCREAMING-DASH-CASE.

func ToKebab

func ToKebab(s string) string

ToKebab returns words in kebab-case (lower case words with dashes). Also known as dash-case.

func ToPascal

func ToPascal(s string) string

ToPascal returns words in PascalCase (capitalized words concatenated together). Also known as UpperPascalCase.

func ToSNAKE

func ToSNAKE(s string) string

ToSNAKE returns words in SNAKE_CASE (upper case words with underscores). Also known as SCREAMING_SNAKE_CASE or UPPER_CASE.

func ToSnake

func ToSnake(s string) string

ToSnake returns words in snake_case (lower case words with underscores).

type Caser

type Caser struct {
    // contains filtered or unexported fields
}

Caser allows for customization of parsing and intialisms

func NewCaser

func NewCaser(goInitialisms bool, initialismOverrides map[string]bool, splitFn SplitFn) *Caser

NewCaser returns a configured Caser.

A Caser should be created when you want fine grained control over how the words are split.

Notes on function arguments

goInitialisms: Whether to use Golint's intialisms

initialismOverrides: A mapping of extra initialisms
Keys must be in ALL CAPS. Merged with Golint's if goInitialisms is set.
Setting a key to false will override Golint's.

splitFn: How to separate words
Override the default split function. Consider using NewSplitFn to
configure one instead of writing your own.

func (*Caser) ToCamel

func (c *Caser) ToCamel(s string) string

ToCamel returns words in camelCase (capitalized words concatenated together, with first word lower case). Also known as lowerCamelCase or mixedCase.

func (*Caser) ToCase

func (c *Caser) ToCase(s string, wordCase WordCase, delimiter rune) string

ToCase returns words with a given case and delimiter.

func (*Caser) ToKEBAB

func (c *Caser) ToKEBAB(s string) string

ToKEBAB returns words in KEBAB-CASE (upper case words with dashes). Also known as SCREAMING-KEBAB-CASE or SCREAMING-DASH-CASE.

func (*Caser) ToKebab

func (c *Caser) ToKebab(s string) string

ToKebab returns words in kebab-case (lower case words with dashes). Also known as dash-case.

func (*Caser) ToPascal

func (c *Caser) ToPascal(s string) string

ToPascal returns words in PascalCase (capitalized words concatenated together). Also known as UpperPascalCase.

func (*Caser) ToSNAKE

func (c *Caser) ToSNAKE(s string) string

ToSNAKE returns words in SNAKE_CASE (upper case words with underscores). Also known as SCREAMING_SNAKE_CASE or UPPER_CASE.

func (*Caser) ToSnake

func (c *Caser) ToSnake(s string) string

ToSnake returns words in snake_case (lower case words with underscores).

type SplitAction

type SplitAction int

SplitAction defines if and how to split a string

const (
    // Noop - Continue to next character
    Noop SplitAction = iota
    // Split - Split between words
    // e.g. to split between wordsWithoutDelimiters
    Split
    // SkipSplit - Split the word and drop the character
    // e.g. to split words with delimiters
    SkipSplit
    // Skip - Remove the character completely
    Skip
)

type SplitFn

type SplitFn func(prev, curr, next rune) SplitAction

SplitFn defines how to split a string into words

func NewSplitFn

func NewSplitFn(
    delimiters []rune,
    splitOptions ...SplitOption,
) SplitFn

NewSplitFn returns a SplitFn based on the options provided.

NewSplitFn covers the majority of common options that other strcase libraries provide and should allow you to simply create a custom caser. For more complicated use cases, feel free to write your own SplitFn nolint:gocyclo

type SplitOption

type SplitOption int

SplitOption are options that allow for configuring NewSplitFn

const (
    // SplitCase - FooBar -> Foo_Bar
    SplitCase SplitOption = iota
    // SplitAcronym - FOOBar -> Foo_Bar
    // It won't preserve FOO's case. If you want, you can set the Caser's initialisms so FOO will be in all caps
    SplitAcronym
    // SplitBeforeNumber - port80 -> port_80
    SplitBeforeNumber
    // SplitAfterNumber - 200status -> 200_status
    SplitAfterNumber
    // PreserveNumberFormatting - a.b.2,000.3.c -> a_b_2,000.3_c
    PreserveNumberFormatting
)

type WordCase

type WordCase int

WordCase is an enumeration of the ways to format a word.

const (
    // Original - Preserve the original input strcase
    Original WordCase = iota
    // LowerCase - All letters lower cased (example)
    LowerCase
    // UpperCase - All letters upper cased (EXAMPLE)
    UpperCase
    // TitleCase - Only first letter upper cased (Example)
    TitleCase
    // CamelCase - TitleCase except lower case first word (exampleText)
    CamelCase
)