matchingSemantics(_:)

Declaration

func matchingSemantics(_ semanticLevel: RegexSemanticLevel) -> Regex<Regex<Output>.RegexOutput>

Parameters

• semanticLevel:

  The semantics to use during matching.

Return Value

The modified regular expression.

Discussion

When matching with grapheme cluster semantics (the default), metacharacters like . and \w, custom character classes, and character class instances like .any match a grapheme cluster when possible, corresponding with the default string representation. In addition, matching with grapheme cluster semantics compares characters using their canonical representation, corresponding with how strings comparison works.

When matching with Unicode scalar semantics, metacharacters and character classes always match a single Unicode scalar value, even if that scalar comprises part of a grapheme cluster.

These semantic levels can lead to different results, especially when working with strings that have decomposed characters. In the following example, queRegex matches any 3-character string that begins with "q".

let composed = "qué"
let decomposed = "que\u{301}"

let queRegex = /^q..$/

print(composed.contains(queRegex))
// Prints "true"
print(decomposed.contains(queRegex))
// Prints "true"

When using Unicode scalar semantics, however, the regular expression only matches the composed version of the string, because each . matches a single Unicode scalar value.

let queRegexScalar = queRegex.matchingSemantics(.unicodeScalar)
print(composed.contains(queRegexScalar))
// Prints "true"
print(decomposed.contains(queRegexScalar))
// Prints "false"