uniseg

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Published: Feb 21, 2023 License: MIT Imports: 1 Imported by: 183

README ¶

Unicode Text Segmentation for Go

Go Reference Go Report

This Go package implements Unicode Text Segmentation according to Unicode Standard Annex #29, Unicode Line Breaking according to Unicode Standard Annex #14 (Unicode version 14.0.0), and monospace font string width calculation similar to wcwidth.

Background

Grapheme Clusters

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
Käse 6 bytes: 4b 61 cc 88 73 65 5 code points: 4b 61 308 73 65 4 clusters: [4b],[61 308],[73],[65]
🏳️‍🌈 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]
🇩🇪 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

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

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

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).

Monospace Width

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.

Installation

go get github.com/rivo/uniseg

Examples

Counting Characters in a String
n := uniseg.GraphemeClusterCount("🇩🇪🏳️‍🌈")
fmt.Println(n)
// 2
Calculating the Monospace String Width
width := uniseg.StringWidth("🇩🇪🏳️‍🌈!")
fmt.Println(width)
// 5
Using the Graphemes Class

This is the most convenient method of iterating over grapheme clusters:

gr := uniseg.NewGraphemes("👍🏼!")
for gr.Next() {
	fmt.Printf("%x ", gr.Runes())
}
// [1f44d 1f3fc] [21]
Using the Step or StepString Function

This is orders of magnitude faster than the Graphemes class, but it requires the handling of states and boundaries:

str := "🇩🇪🏳️‍🌈"
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]
Advanced Examples

Breaking into grapheme clusters and evaluating line breaks:

str := "First line.\nSecond line."
state := -1
var (
	c          string
	boundaries int
)
for len(str) > 0 {
	c, str, boundaries, state = uniseg.StepString(str, state)
	fmt.Print(c)
	if boundaries&uniseg.MaskLine == uniseg.LineCanBreak {
		fmt.Print("|")
	} else if boundaries&uniseg.MaskLine == uniseg.LineMustBreak {
		fmt.Print("‖")
	}
}
// First |line.
// ‖Second |line.‖

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

Finally, if you need to reverse a string while preserving grapheme clusters, use ReverseString:

fmt.Println(uniseg.ReverseString("🇩🇪🏳️‍🌈"))
// 🏳️‍🌈🇩🇪

Documentation

Refer to https://pkg.go.dev/github.com/rivo/uniseg for the package's documentation.

Dependencies

This package does not depend on any packages outside the standard library.

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Your Feedback

Add your issue here on GitHub, preferably before submitting any PR's. Feel free to get in touch if you have any questions.

Documentation ¶

Overview ¶

Package uniseg implements Unicode Text Segmentation, Unicode Line Breaking, and string width calculation for monospace fonts. Unicode Text Segmentation conforms to Unicode Standard Annex #29 (https://unicode.org/reports/tr29/) and Unicode Line Breaking conforms to Unicode Standard Annex #14 (https://unicode.org/reports/tr14/).

In short, using this package, you can split a string into grapheme clusters (what people would usually refer to as a "character"), into words, and into sentences. Or, in its simplest case, this package allows you to count the number of characters in a string, especially when it contains complex characters such as emojis, combining characters, or characters from Asian, Arabic, Hebrew, or other languages. Additionally, you can use it to implement line breaking (or "word wrapping"), that is, to determine where text can be broken over to the next line when the width of the line is not big enough to fit the entire text. Finally, you can use it to calculate the display width of a string for monospace fonts.

Getting Started ¶

If you just want to count the number of characters in a string, you can use GraphemeClusterCount. If you want to determine the display width of a string, you can use StringWidth. If you want to iterate over a string, you can use Step, StepString, or the Graphemes class (more convenient but less performant). This will provide you with all information: grapheme clusters, word boundaries, sentence boundaries, line breaks, and monospace character widths. The specialized functions FirstGraphemeCluster, FirstGraphemeClusterInString, FirstWord, FirstWordInString, FirstSentence, and FirstSentenceInString can be used if only one type of information is needed.

Grapheme Clusters ¶

Consider the rainbow flag emoji: 🏳️‍🌈. On most modern systems, it appears as one character. But its string representation actually has 14 bytes, so counting bytes (or using len("🏳️‍🌈")) will not work as expected. Counting runes won't, either: The flag has 4 Unicode code points, thus 4 runes. The stdlib function utf8.RuneCountInString("🏳️‍🌈") and len([]rune("🏳️‍🌈")) will both return 4.

The GraphemeClusterCount function will return 1 for the rainbow flag emoji. The Graphemes class and a variety of functions in this package will allow you to split strings into its grapheme clusters.

Word Boundaries ¶

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. This package provides methods for determining word boundaries.

Sentence Boundaries ¶

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 methods for determining sentence boundaries.

Line Breaking ¶

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 methods to determine the positions in a string where a line must be broken, may be broken, or must not be broken.

Monospace Width ¶

Monospace width, as referred to in this package, is the width of a string in a monospace font. This is commonly used in terminal user interfaces or text displays or editors that don't support proportional fonts. A width of 1 corresponds to a single character cell. The C function wcswidth() and its implementation in other programming languages is in widespread use for the same purpose. However, there is no standard for the calculation of such widths, and this package differs from wcswidth() in a number of ways, presumably to generate more visually pleasing results.

To start, we assume that every code point has a width of 1, with the following exceptions:

  • Code points with grapheme cluster break properties Control, CR, LF, Extend, and ZWJ have a width of 0.
  • U+2E3A, Two-Em Dash, has a width of 3.
  • U+2E3B, Three-Em Dash, has a width of 4.
  • Characters with the East-Asian Width properties "Fullwidth" (F) and "Wide" (W) have a width of 2. (Properties "Ambiguous" (A) and "Neutral" (N) both have a width of 1.)
  • Code points with grapheme cluster break property Regional Indicator have a width of 2.
  • Code points with grapheme cluster break property Extended Pictographic have a width of 2, unless their Emoji Presentation flag is "No", in which case the width is 1.

For Hangul grapheme clusters composed of conjoining Jamo and for Regional Indicators (flags), all code points except the first one have a width of 0. For grapheme clusters starting with an Extended Pictographic, any additional code point will force a total width of 2, except if the Variation Selector-15 (U+FE0E) is included, in which case the total width is always 1. Grapheme clusters ending with Variation Selector-16 (U+FE0F) have a width of 2.

Note that whether these widths appear correct depends on your application's render engine, to which extent it conforms to the Unicode Standard, and its choice of font.

Index ¶

Examples ¶

Constants ¶

View Source
const (
	LineDontBreak = iota // You may not break the line here.
	LineCanBreak         // You may or may not break the line here.
	LineMustBreak        // You must break the line here.
)

These constants define whether a given text may be broken into the next line. If the break is optional (LineCanBreak), you may choose to break or not based on your own criteria, for example, if the text has reached the available width.

View Source
const (
	MaskLine     = 3
	MaskWord     = 4
	MaskSentence = 8
)

The bit masks used to extract boundary information returned by Step.

View Source
const ShiftWidth = 4

The number of bits to shift the boundary information returned by Step to obtain the monospace width of the grapheme cluster.

Variables ¶

This section is empty.

Functions ¶

func FirstGraphemeCluster ¶ added in v0.3.0

func FirstGraphemeCluster(b []byte, state int) (cluster, rest []byte, width, newState int)

FirstGraphemeCluster returns the first grapheme cluster found in the given byte slice according to the rules of Unicode Standard Annex #29, Grapheme Cluster Boundaries. This function can be called continuously to extract all grapheme clusters from a byte slice, as illustrated in the example below.

If you don't know the current state, for example when calling the function for the first time, you must pass -1. For consecutive calls, pass the state and rest slice returned by the previous call.

The "rest" slice is the sub-slice of the original byte slice "b" starting after the last byte of the identified grapheme cluster. If the length of the "rest" slice is 0, the entire byte slice "b" has been processed. The "cluster" byte slice is the sub-slice of the input slice containing the identified grapheme cluster.

The returned width is the width of the grapheme cluster for most monospace fonts where a value of 1 represents one character cell.

Given an empty byte slice "b", the function returns nil values.

While slightly less convenient than using the Graphemes class, this function has much better performance and makes no allocations. It lends itself well to large byte slices.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("🇩🇪🏳️‍🌈!")
	state := -1
	var c []byte
	for len(b) > 0 {
		var width int
		c, b, width, state = uniseg.FirstGraphemeCluster(b, state)
		fmt.Println(string(c), width)
	}
}
Output:

🇩🇪 2
🏳️‍🌈 2
! 1

func FirstGraphemeClusterInString ¶ added in v0.3.0

func FirstGraphemeClusterInString(str string, state int) (cluster, rest string, width, newState int)

FirstGraphemeClusterInString is like FirstGraphemeCluster but its input and outputs are strings.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "🇩🇪🏳️‍🌈!"
	state := -1
	var c string
	for len(str) > 0 {
		var width int
		c, str, width, state = uniseg.FirstGraphemeClusterInString(str, state)
		fmt.Println(c, width)
	}
}
Output:

🇩🇪 2
🏳️‍🌈 2
! 1

func FirstLineSegment ¶ added in v0.3.0

func FirstLineSegment(b []byte, state int) (segment, rest []byte, mustBreak bool, newState int)

FirstLineSegment returns the prefix of the given byte slice after which a decision to break the string over to the next line can or must be made, according to the rules of Unicode Standard Annex #14. This is used to implement line breaking.

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.

The returned "segment" may not be broken into smaller parts, unless no other breaking opportunities present themselves, in which case you may break by grapheme clusters (using the FirstGraphemeCluster function to determine the grapheme clusters).

The "mustBreak" flag indicates whether you MUST break the line after the given segment (true), for example after newline characters, or you MAY break the line after the given segment (false).

This function can be called continuously to extract all non-breaking sub-sets from a byte slice, as illustrated in the example below.

If you don't know the current state, for example when calling the function for the first time, you must pass -1. For consecutive calls, pass the state and rest slice returned by the previous call.

The "rest" slice is the sub-slice of the original byte slice "b" starting after the last byte of the identified line segment. If the length of the "rest" slice is 0, the entire byte slice "b" has been processed. The "segment" byte slice is the sub-slice of the input slice containing the identified line segment.

Given an empty byte slice "b", the function returns nil values.

Note that in accordance with UAX #14 LB3, the final segment will end with "mustBreak" set to true. You can choose to ignore this by checking if the length of the "rest" slice is 0 and calling HasTrailingLineBreak or HasTrailingLineBreakInString on the last rune.

Note also that this algorithm may break within grapheme clusters. This is addressed in Section 8.2 Example 6 of UAX #14. To avoid this, you can use the Step function instead.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("First line.\nSecond line.")
	state := -1
	var (
		c         []byte
		mustBreak bool
	)
	for len(b) > 0 {
		c, b, mustBreak, state = uniseg.FirstLineSegment(b, state)
		fmt.Printf("(%s)", string(c))
		if mustBreak {
			fmt.Print("!")
		}
	}
}
Output:

(First )(line.
)!(Second )(line.)!

func FirstLineSegmentInString ¶ added in v0.3.0

func FirstLineSegmentInString(str string, state int) (segment, rest string, mustBreak bool, newState int)

FirstLineSegmentInString is like FirstLineSegment() but its input and outputs are strings.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "First line.\nSecond line."
	state := -1
	var (
		c         string
		mustBreak bool
	)
	for len(str) > 0 {
		c, str, mustBreak, state = uniseg.FirstLineSegmentInString(str, state)
		fmt.Printf("(%s)", c)
		if mustBreak {
			fmt.Println(" < must break")
		} else {
			fmt.Println(" < may break")
		}
	}
}
Output:

(First ) < may break
(line.
) < must break
(Second ) < may break
(line.) < must break

func FirstSentence ¶ added in v0.3.0

func FirstSentence(b []byte, state int) (sentence, rest []byte, newState int)

FirstSentence returns the first sentence found in the given byte slice according to the rules of Unicode Standard Annex #29, Sentence Boundaries. This function can be called continuously to extract all sentences from a byte slice, as illustrated in the example below.

If you don't know the current state, for example when calling the function for the first time, you must pass -1. For consecutive calls, pass the state and rest slice returned by the previous call.

The "rest" slice is the sub-slice of the original byte slice "b" starting after the last byte of the identified sentence. If the length of the "rest" slice is 0, the entire byte slice "b" has been processed. The "sentence" byte slice is the sub-slice of the input slice containing the identified sentence.

Given an empty byte slice "b", the function returns nil values.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("This is sentence 1.0. And this is sentence two.")
	state := -1
	var c []byte
	for len(b) > 0 {
		c, b, state = uniseg.FirstSentence(b, state)
		fmt.Printf("(%s)\n", string(c))
	}
}
Output:

(This is sentence 1.0. )
(And this is sentence two.)

func FirstSentenceInString ¶ added in v0.3.0

func FirstSentenceInString(str string, state int) (sentence, rest string, newState int)

FirstSentenceInString is like FirstSentence but its input and outputs are strings.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "This is sentence 1.0. And this is sentence two."
	state := -1
	var c string
	for len(str) > 0 {
		c, str, state = uniseg.FirstSentenceInString(str, state)
		fmt.Printf("(%s)\n", c)
	}
}
Output:

(This is sentence 1.0. )
(And this is sentence two.)

func FirstWord ¶ added in v0.3.0

func FirstWord(b []byte, state int) (word, rest []byte, newState int)

FirstWord returns the first word found in the given byte slice according to the rules of Unicode Standard Annex #29, Word Boundaries. This function can be called continuously to extract all words from a byte slice, as illustrated in the example below.

If you don't know the current state, for example when calling the function for the first time, you must pass -1. For consecutive calls, pass the state and rest slice returned by the previous call.

The "rest" slice is the sub-slice of the original byte slice "b" starting after the last byte of the identified word. If the length of the "rest" slice is 0, the entire byte slice "b" has been processed. The "word" byte slice is the sub-slice of the input slice containing the identified word.

Given an empty byte slice "b", the function returns nil values.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("Hello, world!")
	state := -1
	var c []byte
	for len(b) > 0 {
		c, b, state = uniseg.FirstWord(b, state)
		fmt.Printf("(%s)\n", string(c))
	}
}
Output:

(Hello)
(,)
( )
(world)
(!)

func FirstWordInString ¶ added in v0.3.0

func FirstWordInString(str string, state int) (word, rest string, newState int)

FirstWordInString is like FirstWord but its input and outputs are strings.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "Hello, world!"
	state := -1
	var c string
	for len(str) > 0 {
		c, str, state = uniseg.FirstWordInString(str, state)
		fmt.Printf("(%s)\n", c)
	}
}
Output:

(Hello)
(,)
( )
(world)
(!)

func GraphemeClusterCount ¶

func GraphemeClusterCount(s string) (n int)

GraphemeClusterCount returns the number of user-perceived characters (grapheme clusters) for the given string.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	n := uniseg.GraphemeClusterCount("🇩🇪🏳️‍🌈")
	fmt.Println(n)
}
Output:

2

func HasTrailingLineBreak ¶ added in v0.3.4

func HasTrailingLineBreak(b []byte) bool

HasTrailingLineBreak returns true if the last rune in the given byte slice is one of the hard line break code points defined in LB4 and LB5 of UAX #14.

func HasTrailingLineBreakInString ¶ added in v0.3.4

func HasTrailingLineBreakInString(str string) bool

HasTrailingLineBreakInString is like HasTrailingLineBreak but for a string.

func ReverseString ¶ added in v0.4.3

func ReverseString(s string) string

ReverseString reverses the given string while observing grapheme cluster boundaries.

func Step ¶ added in v0.3.0

func Step(b []byte, state int) (cluster, rest []byte, boundaries int, newState int)

Step returns the first grapheme cluster (user-perceived character) found in the given byte slice. It also returns information about the boundary between that grapheme cluster and the one following it as well as the monospace width of the grapheme cluster. There are three types of boundary information: word boundaries, sentence boundaries, and line breaks. This function is therefore a combination of FirstGraphemeCluster, FirstWord, FirstSentence, and FirstLineSegment.

The "boundaries" return value can be evaluated as follows:

  • boundaries&MaskWord != 0: The boundary is a word boundary.
  • boundaries&MaskWord == 0: The boundary is not a word boundary.
  • boundaries&MaskSentence != 0: The boundary is a sentence boundary.
  • boundaries&MaskSentence == 0: The boundary is not a sentence boundary.
  • boundaries&MaskLine == LineDontBreak: You must not break the line at the boundary.
  • boundaries&MaskLine == LineMustBreak: You must break the line at the boundary.
  • boundaries&MaskLine == LineCanBreak: You may or may not break the line at the boundary.
  • boundaries >> ShiftWidth: The width of the grapheme cluster for most monospace fonts where a value of 1 represents one character cell.

This function can be called continuously to extract all grapheme clusters from a byte slice, as illustrated in the examples below.

If you don't know which state to pass, for example when calling the function for the first time, you must pass -1. For consecutive calls, pass the state and rest slice returned by the previous call.

The "rest" slice is the sub-slice of the original byte slice "b" starting after the last byte of the identified grapheme cluster. If the length of the "rest" slice is 0, the entire byte slice "b" has been processed. The "cluster" byte slice is the sub-slice of the input slice containing the first identified grapheme cluster.

Given an empty byte slice "b", the function returns nil values.

While slightly less convenient than using the Graphemes class, this function has much better performance and makes no allocations. It lends itself well to large byte slices.

Note that in accordance with UAX #14 LB3, the final segment will end with a mandatory line break (boundaries&MaskLine == LineMustBreak). You can choose to ignore this by checking if the length of the "rest" slice is 0 and calling HasTrailingLineBreak or HasTrailingLineBreakInString on the last rune.

Example (Graphemes) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("🇩🇪🏳️‍🌈!")
	state := -1
	var c []byte
	for len(b) > 0 {
		var boundaries int
		c, b, boundaries, state = uniseg.Step(b, state)
		fmt.Println(string(c), boundaries>>uniseg.ShiftWidth)
	}
}
Output:

🇩🇪 2
🏳️‍🌈 2
! 1
Example (LineBreaking) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("First line.\nSecond line.")
	state := -1
	var (
		c          []byte
		boundaries int
	)
	for len(b) > 0 {
		c, b, boundaries, state = uniseg.Step(b, state)
		fmt.Print(string(c))
		if boundaries&uniseg.MaskLine == uniseg.LineCanBreak {
			fmt.Print("|")
		} else if boundaries&uniseg.MaskLine == uniseg.LineMustBreak {
			fmt.Print("‖")
		}
	}
}
Output:

First |line.
‖Second |line.‖
Example (Sentence) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("This is sentence 1.0. And this is sentence two.")
	state := -1
	var (
		c          []byte
		boundaries int
	)
	for len(b) > 0 {
		c, b, boundaries, state = uniseg.Step(b, state)
		fmt.Print(string(c))
		if boundaries&uniseg.MaskSentence != 0 {
			fmt.Print("|")
		}
	}
}
Output:

This is sentence 1.0. |And this is sentence two.|
Example (Word) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	b := []byte("Hello, world!")
	state := -1
	var (
		c          []byte
		boundaries int
	)
	for len(b) > 0 {
		c, b, boundaries, state = uniseg.Step(b, state)
		fmt.Print(string(c))
		if boundaries&uniseg.MaskWord != 0 {
			fmt.Print("|")
		}
	}
}
Output:

Hello|,| |world|!|

func StepString ¶ added in v0.3.0

func StepString(str string, state int) (cluster, rest string, boundaries int, newState int)

StepString is like Step but its input and outputs are strings.

Example (Graphemes) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "🇩🇪🏳️‍🌈!"
	state := -1
	var c string
	for len(str) > 0 {
		var boundaries int
		c, str, boundaries, state = uniseg.StepString(str, state)
		fmt.Println(c, boundaries>>uniseg.ShiftWidth)
	}
}
Output:

🇩🇪 2
🏳️‍🌈 2
! 1
Example (LineBreaking) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "First line.\nSecond line."
	state := -1
	var (
		c          string
		boundaries int
	)
	for len(str) > 0 {
		c, str, boundaries, state = uniseg.StepString(str, state)
		fmt.Print(c)
		if boundaries&uniseg.MaskLine == uniseg.LineCanBreak {
			fmt.Print("|")
		} else if boundaries&uniseg.MaskLine == uniseg.LineMustBreak {
			fmt.Print("‖")
		}
	}
}
Output:

First |line.
‖Second |line.‖
Example (Sentence) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "This is sentence 1.0. And this is sentence two."
	state := -1
	var (
		c          string
		boundaries int
	)
	for len(str) > 0 {
		c, str, boundaries, state = uniseg.StepString(str, state)
		fmt.Print(c)
		if boundaries&uniseg.MaskSentence != 0 {
			fmt.Print("|")
		}
	}
}
Output:

This is sentence 1.0. |And this is sentence two.|
Example (Word) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	str := "Hello, world!"
	state := -1
	var (
		c          string
		boundaries int
	)
	for len(str) > 0 {
		c, str, boundaries, state = uniseg.StepString(str, state)
		fmt.Print(c)
		if boundaries&uniseg.MaskWord != 0 {
			fmt.Print("|")
		}
	}
}
Output:

Hello|,| |world|!|

func StringWidth ¶ added in v0.4.0

func StringWidth(s string) (width int)

StringWidth returns the monospace width for the given string, that is, the number of same-size cells to be occupied by the string.

Example ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	fmt.Println(uniseg.StringWidth("Hello, 世界"))
}
Output:

11

Types ¶

type Graphemes ¶

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

Graphemes implements an iterator over Unicode grapheme clusters, or user-perceived characters. While iterating, it also provides information about word boundaries, sentence boundaries, line breaks, and monospace character widths.

After constructing the class via NewGraphemes for a given string "str", Graphemes.Next is called for every grapheme cluster in a loop until it returns false. Inside the loop, information about the grapheme cluster as well as boundary information and character width is available via the various methods (see examples below).

Using this class to iterate over a string is convenient but it is much slower than using this package's Step or StepString functions or any of the other specialized functions starting with "First".

Example (Graphemes) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	g := uniseg.NewGraphemes("🇩🇪🏳️‍🌈")
	for g.Next() {
		fmt.Println(g.Str())
	}
}
Output:

🇩🇪
🏳️‍🌈
Example (LineBreaking) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	g := uniseg.NewGraphemes("First line.\nSecond line.")
	for g.Next() {
		fmt.Print(g.Str())
		if g.LineBreak() == uniseg.LineCanBreak {
			fmt.Print("|")
		} else if g.LineBreak() == uniseg.LineMustBreak {
			fmt.Print("‖")
		}
	}
}
Output:

First |line.
‖Second |line.‖
Example (Sentence) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	g := uniseg.NewGraphemes("This is sentence 1.0. And this is sentence two.")
	for g.Next() {
		fmt.Print(g.Str())
		if g.IsSentenceBoundary() {
			fmt.Print("|")
		}
	}
}
Output:

This is sentence 1.0. |And this is sentence two.|
Example (Word) ¶
package main

import (
	"fmt"

	"github.com/rivo/uniseg"
)

func main() {
	g := uniseg.NewGraphemes("Hello, world!")
	for g.Next() {
		fmt.Print(g.Str())
		if g.IsWordBoundary() {
			fmt.Print("|")
		}
	}
}
Output:

Hello|,| |world|!|

func NewGraphemes ¶

func NewGraphemes(str string) *Graphemes

NewGraphemes returns a new grapheme cluster iterator.

func (*Graphemes) Bytes ¶

func (g *Graphemes) Bytes() []byte

Bytes returns a byte slice which corresponds to the current grapheme cluster. If the iterator is already past the end or Graphemes.Next has not yet been called, nil is returned.

func (*Graphemes) IsSentenceBoundary ¶ added in v0.3.0

func (g *Graphemes) IsSentenceBoundary() bool

IsSentenceBoundary returns true if a sentence ends after the current grapheme cluster.

func (*Graphemes) IsWordBoundary ¶ added in v0.3.0

func (g *Graphemes) IsWordBoundary() bool

IsWordBoundary returns true if a word ends after the current grapheme cluster.

func (*Graphemes) LineBreak ¶ added in v0.3.0

func (g *Graphemes) LineBreak() int

LineBreak returns whether the line can be broken after the current grapheme cluster. A value of LineDontBreak means the line may not be broken, a value of LineMustBreak means the line must be broken, and a value of LineCanBreak means the line may or may not be broken.

func (*Graphemes) Next ¶

func (g *Graphemes) Next() bool

Next advances the iterator by one grapheme cluster and returns false if no clusters are left. This function must be called before the first cluster is accessed.

func (*Graphemes) Positions ¶

func (g *Graphemes) Positions() (int, int)

Positions returns the interval of the current grapheme cluster as byte positions into the original string. The first returned value "from" indexes the first byte and the second returned value "to" indexes the first byte that is not included anymore, i.e. str[from:to] is the current grapheme cluster of the original string "str". If Graphemes.Next has not yet been called, both values are 0. If the iterator is already past the end, both values are 1.

func (*Graphemes) Reset ¶

func (g *Graphemes) Reset()

Reset puts the iterator into its initial state such that the next call to Graphemes.Next sets it to the first grapheme cluster again.

func (*Graphemes) Runes ¶

func (g *Graphemes) Runes() []rune

Runes returns a slice of runes (code points) which corresponds to the current grapheme cluster. If the iterator is already past the end or Graphemes.Next has not yet been called, nil is returned.

func (*Graphemes) Str ¶

func (g *Graphemes) Str() string

Str returns a substring of the original string which corresponds to the current grapheme cluster. If the iterator is already past the end or Graphemes.Next has not yet been called, an empty string is returned.

func (*Graphemes) Width ¶ added in v0.4.0

func (g *Graphemes) Width() int

Width returns the monospace width of the current grapheme cluster.

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