I'm using swift to learn regex. I don't know why the wholeMatch method return nil, but the matches is correct.

var statement =
"""
CREDIT    04062020    PayPal transfer    $4.99
CREDIT    04032020    Payroll            $69.73
DEBIT     04022020    ACH transfer       $38.25
DEBIT     03242020    IRS tax payment    $52249.98
"""

enum TransactionKind: String {
    case credit = "CREDIT"
    case debit = "DEBIT"
}

struct Date {
    var month, day, year: Int
    init?(mmddyyyy: String) {
        self.month = 1
        self.day = 1
        self.year = 2022
    }
}

struct Amount {
    var valueTimes100: Int = 0
    init?(twoDecimalPlaces text: Substring) {
        self.valueTimes100 = Int(100 * (Float(text) ?? 0))
    }
}

let statementPattern = Regex {
    TryCapture {
        ChoiceOf {
            "CREDIT"
            "DEBIT"
        }
    } transform: {
        TransactionKind(rawValue: String($0))
    }
    OneOrMore(.whitespace)
    TryCapture {
        Repeat(.digit, count: 2)
        Repeat(.digit, count: 2)
        Repeat(.digit, count: 4)
    } transform: { Date(mmddyyyy: String($0)) }
    OneOrMore(.whitespace)
    Capture {
        OneOrMore(CharacterClass(.word, .whitespace))
        CharacterClass.word
    } transform: {
        String($0)
    }
    OneOrMore(.whitespace)
    "$"
    TryCapture {
        OneOrMore(.digit)
        "."
        Repeat(.digit, count: 2)
    } transform: {
        Amount(twoDecimalPlaces: $0)
    }
}

let results = try? statementPattern.wholeMatch(in: statement)
print(results) // print nil
                                               
for match in statement.matches(of: statementPattern) {
    let (line, kind, date, description, amount) = match.output
    print(description) // can correct print
}

CodePudding user response：

wholeMatch means that the pattern must match the entire string.

It's the equivalent of a literal pattern which starts with ^ and ends with $.

You can prove it by removing three lines in the string.