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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 ( and Unicode Line Breaking conforms to Unicode Standard Annex #14 ( 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. 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. Consider the rainbow flag emoji: ๐Ÿณ๏ธโ€๐ŸŒˆ. On most modern systems, it appears as one character. But its string representation actually has 14 bytes, so counting bytes (or using len("๐Ÿณ๏ธโ€๐ŸŒˆ")) 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("๐Ÿณ๏ธโ€๐ŸŒˆ") and len([]rune("๐Ÿณ๏ธโ€๐ŸŒˆ")) 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 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 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, 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, 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: 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.


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Last updated on 20 Nov 2022

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