An implementation of grapheme cluster boundaries from Unicode text segmentation (UAX 29), for Unicode version 15.0.0.

Quick start

go get "github.com/clipperhouse/uax29/v2/graphemes"

import "github.com/clipperhouse/uax29/v2/graphemes"

text := "Hello, 世界. Nice dog! 👍🐶"

tokens := graphemes.FromString(text)

for tokens.Next() {                     // Next() returns true until end of data
	fmt.Println(tokens.Value())         // Do something with the current grapheme
}

A grapheme is a “single visible character”, which might be a simple as a single letter, or a complex emoji that consists of several Unicode code points.

Conformance

We use the Unicode test suite.

APIs

If you have a string

text := "Hello, 世界. Nice dog! 👍🐶"

tokens := graphemes.FromString(text)

for tokens.Next() {                     // Next() returns true until end of data
	fmt.Println(tokens.Value())         // Do something with the current grapheme
}

If you have an io.Reader

FromReader embeds a bufio.Scanner, so just use those methods.

r := getYourReader()                        // from a file or network maybe
tokens := graphemes.FromReader(r)

for tokens.Scan() {                         // Scan() returns true until error or EOF
	fmt.Println(tokens.Text())              // Do something with the current grapheme
}

if tokens.Err() != nil {                    // Check the error
	log.Fatal(tokens.Err())
}

If you have a []byte

b := []byte("Hello, 世界. Nice dog! 👍🐶")

tokens := graphemes.FromBytes(b)

for tokens.Next() {                     // Next() returns true until end of data
	fmt.Println(tokens.Value())         // Do something with the current grapheme
}

Benchmarks

On a Mac M2 laptop, we see around 200MB/s, or around 100 million graphemes per second, and no allocations.

goos: darwin
goarch: arm64
pkg: github.com/clipperhouse/uax29/graphemes/comparative
cpu: Apple M2
BenchmarkGraphemes/clipperhouse/uax29-8    	    173805 ns/op	 201.16 MB/s      0 B/op	   0 allocs/op
BenchmarkGraphemes/rivo/uniseg-8           	   2045128 ns/op	  17.10 MB/s      0 B/op	   0 allocs/op

Invalid inputs

Invalid UTF-8 input is considered undefined behavior. We test to ensure that bad inputs will not cause pathological outcomes, such as a panic or infinite loop. Callers should expect “garbage-in, garbage-out”.

Your pipeline should probably include a call to utf8.Valid().