Given a character (e.g. 
), how do I find the character that's immediately greater or lesser than it?
There is a finite number of Unicode characters, and Character conforms to Comparable. So there must be a character that immediately precedes or succeeds , and a way to find it. However, I am not able find much information about it in Character's source, in which character comparison is just delegated to string comparison:
extension Character: Comparable {
@inlinable @inline(__always)
@_effects(readonly)
public static func < (lhs: Character, rhs: Character) -> Bool {
return lhs._str < rhs._str
}
}
There is an infinite number of possible Character instances (extended grapheme clusters in Unicode parlance). a + (◌́ × ∞) is still a single Character. That means there is no such thing as “the character before b”.
There is a finite number of Unicode scalars (Unicode.Scalar, element of String.UnicodeScalarView, accessible through myString.unicodeScalars). If that is what you want to use, you can take the UInt32 value of a scalar and then keep incrementing it until backwards initialization from the integer value succeeds. But that strategy won’t match any meaningful sort order expected by humans; the order they were encoded is (mostly) just a fluke of history. The strategy also won’t match the behaviour of String’s Comparable conformance, since á and a + ◌́ are different scalar sequences but still equal strings.
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Thanks! I forgot that you can use combining characters recursively. I guess the premise to my question is invalid then.
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