prefixMatch(in:)

Declaration

func prefixMatch(in string: Substring) throws -> Regex<Output>.Match?

Parameters

• string:

  The substring to match this regular expression against.

Return Value

The match, if this regex matches at the start of string; otherwise, nil.

Discussion

Call this method if you want the regular expression to succeed only when it matches only at the start of the given string. This example uses prefixMatch(in:) and a regex that matches a title-case word to search for such a word at the start of different strings:

let titleCaseWord = /[A-Z][A-Za-z]+/

if let wordMatch = try titleCaseWord.prefixMatch(in: "Searching in a Regex") {
    print(wordMatch.0)
} else {
    print("No match.")
}
// Prints "Searching"

if let wordMatch = try titleCaseWord.prefixMatch(in: "title case word at the End") {
    print(wordMatch.0)
} else {
    print("No match.")
}
// Prints "No match."

The prefixMatch(in:) method can throw an error if this regex includes a transformation closure that throws an error.