This Go package implements Unicode Text Segmentation according to Unicode Standard Annex #29, Unicode Line Breaking according to Unicode Standard Annex #14 (Unicode version 15.0.0), and monospace font string width calculation similar to wcwidth.
In Go, strings are read-only slices of bytes. They can be turned into Unicode code points using the for loop or by casting: []rune(str). However, multiple code points may be combined into one user-perceived character or what the Unicode specification calls "grapheme cluster". Here are some examples:
| String | Bytes (UTF-8) | Code points (runes) | Grapheme clusters |
|---|---|---|---|
| Kaฬse | 6 bytes: 4b 61 cc 88 73 65 |
5 code points: 4b 61 308 73 65 |
4 clusters: [4b],[61 308],[73],[65] |
| ๐ณ๏ธโ๐ | 14 bytes: f0 9f 8f b3 ef b8 8f e2 80 8d f0 9f 8c 88 |
4 code points: 1f3f3 fe0f 200d 1f308 |
1 cluster: [1f3f3 fe0f 200d 1f308] |
| ๐ฉ๐ช | 8 bytes: f0 9f 87 a9 f0 9f 87 aa |
2 code points: 1f1e9 1f1ea |
1 cluster: [1f1e9 1f1ea] |
This package provides tools to iterate over these grapheme clusters. This may be used to determine the number of user-perceived characters, to split strings in their intended places, or to extract individual characters which form a unit.
Word boundaries are used in a number of different contexts. The most familiar ones are selection (double-click mouse selection), cursor movement ("move to next word" control-arrow keys), and the dialog option "Whole Word Search" for search and replace. They are also used in database queries, to determine whether elements are within a certain number of words of one another. Searching may also use word boundaries in determining matching items. This package provides tools to determine word boundaries within strings.
Sentence boundaries are often used for triple-click or some other method of selecting or iterating through blocks of text that are larger than single words. They are also used to determine whether words occur within the same sentence in database queries. This package provides tools to determine sentence boundaries within strings.
Line breaking, also known as word wrapping, is the process of breaking a section of text into lines such that it will fit in the available width of a page, window or other display area. This package provides tools to determine where a string may or may not be broken and where it must be broken (for example after newline characters).
Most terminals or text displays / text editors using a monospace font (for example source code editors) use a fixed width for each character. Some characters such as emojis or characters found in Asian and other languages may take up more than one character cell. This package provides tools to determine the number of cells a string will take up when displayed in a monospace font. See here for more information.
go get github.com/rivo/unisegn := uniseg.GraphemeClusterCount("๐ฉ๐ช๐ณ๏ธโ๐")
fmt.Println(n)
// 2width := uniseg.StringWidth("๐ฉ๐ช๐ณ๏ธโ๐!")
fmt.Println(width)
// 5Using the Graphemes Class
This is the most convenient method of iterating over grapheme clusters:
gr := uniseg.NewGraphemes("๐๐ผ!")
for gr.Next() {
fmt.Printf("%x ", gr.Runes())
}
// [1f44d 1f3fc] [21]Using the Step or StepString Function
This avoids allocating a new Graphemes object but it requires the handling of states and boundaries:
str := "๐ฉ๐ช๐ณ๏ธโ๐"
state := -1
var c string
for len(str) > 0 {
c, str, _, state = uniseg.StepString(str, state)
fmt.Printf("%x ", []rune(c))
}
// [1f1e9 1f1ea] [1f3f3 fe0f 200d 1f308]The Graphemes class offers the most convenient way to access all functionality of this package. But in some cases, it may be better to use the specialized functions directly. For example, if you're only interested in word segmentation, use FirstWord or FirstWordInString:
str := "Hello, world!"
state := -1
var c string
for len(str) > 0 {
c, str, state = uniseg.FirstWordInString(str, state)
fmt.Printf("(%s)\n", c)
}
// (Hello)
// (,)
// ( )
// (world)
// (!)Similarly, use
FirstGraphemeClusterorFirstGraphemeClusterInStringfor grapheme cluster determination only,FirstSentenceorFirstSentenceInStringfor sentence segmentation only, andFirstLineSegmentorFirstLineSegmentInStringfor line breaking / word wrapping (although usingSteporStepStringis preferred as it will observe grapheme cluster boundaries).
If you're only interested in the width of characters, use FirstGraphemeCluster or FirstGraphemeClusterInString. It is much faster than using Step, StepString, or the Graphemes class because it does not include the logic for word / sentence / line boundaries.
Finally, if you need to reverse a string while preserving grapheme clusters, use ReverseString:
fmt.Println(uniseg.ReverseString("๐ฉ๐ช๐ณ๏ธโ๐"))
// ๐ณ๏ธโ๐๐ฉ๐ชRefer to https://pkg.go.dev/github.com/rivo/uniseg for the package's documentation.
This package does not depend on any packages outside the standard library.
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