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109 lines
5.3 KiB
Go
109 lines
5.3 KiB
Go
/*
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Package uniseg implements Unicode Text Segmentation, Unicode Line Breaking, and
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string width calculation for monospace fonts. Unicode Text Segmentation conforms
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to Unicode Standard Annex #29 (https://unicode.org/reports/tr29/) and Unicode
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Line Breaking conforms to Unicode Standard Annex #14
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(https://unicode.org/reports/tr14/).
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In short, using this package, you can split a string into grapheme clusters
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(what people would usually refer to as a "character"), into words, and into
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sentences. Or, in its simplest case, this package allows you to count the number
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of characters in a string, especially when it contains complex characters such
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as emojis, combining characters, or characters from Asian, Arabic, Hebrew, or
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other languages. Additionally, you can use it to implement line breaking (or
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"word wrapping"), that is, to determine where text can be broken over to the
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next line when the width of the line is not big enough to fit the entire text.
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Finally, you can use it to calculate the display width of a string for monospace
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fonts.
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# Getting Started
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If you just want to count the number of characters in a string, you can use
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[GraphemeClusterCount]. If you want to determine the display width of a string,
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you can use [StringWidth]. If you want to iterate over a string, you can use
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[Step], [StepString], or the [Graphemes] class (more convenient but less
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performant). This will provide you with all information: grapheme clusters,
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word boundaries, sentence boundaries, line breaks, and monospace character
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widths. The specialized functions [FirstGraphemeCluster],
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[FirstGraphemeClusterInString], [FirstWord], [FirstWordInString],
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[FirstSentence], and [FirstSentenceInString] can be used if only one type of
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information is needed.
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# Grapheme Clusters
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Consider the rainbow flag emoji: 🏳️🌈. On most modern systems, it appears as one
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character. But its string representation actually has 14 bytes, so counting
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bytes (or using len("🏳️🌈")) will not work as expected. Counting runes won't,
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either: The flag has 4 Unicode code points, thus 4 runes. The stdlib function
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utf8.RuneCountInString("🏳️🌈") and len([]rune("🏳️🌈")) will both return 4.
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The [GraphemeClusterCount] function will return 1 for the rainbow flag emoji.
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The Graphemes class and a variety of functions in this package will allow you to
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split strings into its grapheme clusters.
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# Word Boundaries
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Word boundaries are used in a number of different contexts. The most familiar
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ones are selection (double-click mouse selection), cursor movement ("move to
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next word" control-arrow keys), and the dialog option "Whole Word Search" for
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search and replace. This package provides methods for determining word
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boundaries.
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# Sentence Boundaries
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Sentence boundaries are often used for triple-click or some other method of
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selecting or iterating through blocks of text that are larger than single words.
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They are also used to determine whether words occur within the same sentence in
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database queries. This package provides methods for determining sentence
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boundaries.
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# Line Breaking
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Line breaking, also known as word wrapping, is the process of breaking a section
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of text into lines such that it will fit in the available width of a page,
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window or other display area. This package provides methods to determine the
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positions in a string where a line must be broken, may be broken, or must not be
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broken.
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# Monospace Width
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Monospace width, as referred to in this package, is the width of a string in a
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monospace font. This is commonly used in terminal user interfaces or text
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displays or editors that don't support proportional fonts. A width of 1
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corresponds to a single character cell. The C function [wcswidth()] and its
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implementation in other programming languages is in widespread use for the same
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purpose. However, there is no standard for the calculation of such widths, and
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this package differs from wcswidth() in a number of ways, presumably to generate
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more visually pleasing results.
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To start, we assume that every code point has a width of 1, with the following
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exceptions:
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- Code points with grapheme cluster break properties Control, CR, LF, Extend,
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and ZWJ have a width of 0.
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- U+2E3A, Two-Em Dash, has a width of 3.
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- U+2E3B, Three-Em Dash, has a width of 4.
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- Characters with the East-Asian Width properties "Fullwidth" (F) and "Wide"
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(W) have a width of 2. (Properties "Ambiguous" (A) and "Neutral" (N) both
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have a width of 1.)
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- Code points with grapheme cluster break property Regional Indicator have a
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width of 2.
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- Code points with grapheme cluster break property Extended Pictographic have
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a width of 2, unless their Emoji Presentation flag is "No", in which case
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the width is 1.
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For Hangul grapheme clusters composed of conjoining Jamo and for Regional
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Indicators (flags), all code points except the first one have a width of 0. For
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grapheme clusters starting with an Extended Pictographic, any additional code
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point will force a total width of 2, except if the Variation Selector-15
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(U+FE0E) is included, in which case the total width is always 1. Grapheme
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clusters ending with Variation Selector-16 (U+FE0F) have a width of 2.
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Note that whether these widths appear correct depends on your application's
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render engine, to which extent it conforms to the Unicode Standard, and its
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choice of font.
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[wcswidth()]: https://man7.org/linux/man-pages/man3/wcswidth.3.html
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*/
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package uniseg
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