String::Grapheme

Grapheme represents a Unicode grapheme cluster, which describes the smallest functional unit of a writing system. This is also called a user-perceived character.

In the latin alphabet, most graphemes consist of a single Unicode codepoint (equivalent to Char). But a grapheme can also consist of a sequence of codepoints, which combine into a single unit.

For example, the string "e\u0301" consists of two characters, the latin small letter e and the combining acute accent ´. Together, they form a single grapheme: é. That same grapheme could alternatively be described in a single codepoint, \u00E9 (latin small letter e with acute). But the combinatory possibilities are far bigger than the amount of directly available codepoints.

"e\u0301".size # => 2
"é".size       # => 1

"e\u0301".grapheme_size # => 1
"é".grapheme_size       # => 1

This combination of codepoints is common in some non-latin scripts. It's also often used with emojis to create customized combination. For example, the thumbs up sign 👍 (U+1F44D) combined with an emoji modifier such as U+1F3FC assign a colour to the emoji.

Instances of this type can be acquired via String#each_grapheme or String#graphemes.

The algorithm to determine boundaries between grapheme clusters is specified in the Unicode Standard Annex #29.