Converting string to Bool and testing for IF statement in Swift

Question

So I am trying to take thee first index of a string (fullName) and test it to see if it matches all vowels lower and uppercased... for some reason when I use the .startIndex I test one letter at a time with a If statement.

Ia there a way to test all vowels at once ()I tried || in between each and it gave me the error "cannot convert string to Bool". Appreciate any help.

func lyricsForName(lyricsTemplate: String, fullName: String) -> String {

    let shortName = shortNameFromName(name: fullName)
    let index = fullName[fullName.startIndex]
    if index== ("a","A"){

        let lyrics = lyricsTemplate
            .replacingOccurrences(of:"<FULL_NAME>", with: fullName)
            .replacingOccurrences (of:"<SHORT_NAME>", with: fullName )

        return lyrics
    }else{
        let lyrics = lyricsTemplate
            .replacingOccurrences(of:"<FULL_NAME>", with: fullName)
            .replacingOccurrences (of:"<SHORT_NAME>", with: shortName )

        return lyrics

index it is not a good name for a character. if String(fullName.characters.prefix(1)).uppercased() == "A" — Leo Dabus
– Leo Dabus, Commented Jan 31, 2017 at 3:00

GetSwifty · Accepted Answer · 2017-01-31 04:22:35Z

1

You can do it as previously answered, but this is a more Swifty way using the available APIs:

extension String {
    var firstThreeLettersAreVowels: Bool {
        guard characters.count >= 3 else {
            return false
        }

        let firstThreeLetters = substring(to: index(startIndex, offsetBy: 3))
        let isAllVowels = CharacterSet(charactersIn: firstThreeLetters).isSubset(of: CharacterSet.vowels)
        return isAllVowels
    }

    var isLower: Bool {
        return CharacterSet(charactersIn: self).isSubset(of: CharacterSet.lowercaseLetters)
    }

    var isUpper: Bool {
        return CharacterSet(charactersIn: self).isDisjoint(with: CharacterSet.lowercaseLetters)
    }
}

extension CharacterSet {
    static var vowels: CharacterSet {
        return CharacterSet(charactersIn: "AEIOUYaeiouy")
    }
}

Or the one liner (without length check) is

extension String {
    var firstThreeLettersAreVowels: Bool {
        return CharacterSet(charactersIn: substring(to: index(startIndex, offsetBy: 3)))
                    .isSubset(of: CharacterSet(charactersIn: "AEIOUYaeiouy"))
    }
}

This allows you rely on existing APIs rather than trying to do the work yourself, and it should be pretty fast.

edited Jan 31, 2017 at 4:22

answered Jan 31, 2017 at 4:17

GetSwifty

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11 Comments

muescha Over a year ago

it think it was a typo thee means the

muescha Over a year ago

anyway this guard is wrong guard characters.count >= 3 else

muescha Over a year ago

it should be check it there are less then 3 letters guard characters.count < 3 else

GetSwifty Over a year ago

The guard is correct. natashatherobot.com/swift-guard-better-than-if

muescha Over a year ago

oh sorry - i mixed it up - yes you are right - i forget it should be true and otherwise it do the else and return false if chars.count one of 0,1,2

|

vacawama · Accepted Answer · 2017-01-31 04:29:46Z

1

Here is one way to do it. You can use an array of vowels and then test if the array contains the first character:

let fullName = "Albert"

let vowels = "aeiouAEIOU".characters    

if let first = fullName.characters.first, vowels.contains(first) {
    print("\(fullName) starts with a vowel")
}

Albert starts with a vowel

Note: Using fullName.characters.first is safer than fullName[fullName.startIndex] because the latter will crash for an empty String.

edited Jan 31, 2017 at 4:29

answered Jan 31, 2017 at 3:19

vacawama

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1 Comment

muescha Over a year ago

and with fullName.characters.first.uppercased you can half the vowels array

Community · Accepted Answer · 2017-05-23 11:53:08Z

all kudos please to PEEJWEEJ answer

the characterset was his idea :)

i made it only more general

import Foundation

extension String {
    func isFirstLetters(count: Int, of characterSet: CharacterSet) -> Bool {

        guard characters.count >= count else {
            return false
        }

        let firstLetters = substring(to: index(startIndex, offsetBy: count))
        let isInSubset = CharacterSet(charactersIn: firstLetters).isSubset(of: characterSet

        )
        return isInSubset
    }
}

extension CharacterSet {
    static var vowels: CharacterSet {
        return CharacterSet(charactersIn: "AEIOUYaeiouy")
    }
}

some Test cases:

"abcDEf".isFirstLetters(count: 3, of: .vowels) // false
"aioDEf".isFirstLetters(count: 3, of: .vowels) // true

"abcDEf".isFirstLetters(count: 1, of: .vowels) // true
"bbcDEf".isFirstLetters(count: 1, of: .vowels) // false
"ibcDEf".isFirstLetters(count: 1, of: .vowels) // true

"ABcdef".isFirstLetters(count: 3, of: .uppercaseLetters) // false
"ABDdef".isFirstLetters(count: 3, of: .uppercaseLetters) // true

"abBABcdef".isFirstLetters(count: 3, of: .lowercaseLetters) // false
"abbABDdef".isFirstLetters(count: 3, of: .lowercaseLetters) // true


"ABD".isFirstLetters(count: 3, of: CharacterSet(charactersIn: "A"..."C")) // false
"ABD".isFirstLetters(count: 3, of: CharacterSet(charactersIn: "A"..."D")) // true

debug info:

extension CharacterSet {
    var characters: [Character] {
        var result: [Character] = []
        for plane: UInt8 in 0...16 where self.hasMember(inPlane: plane) {
            for unicode in UInt32(plane) << 16 ..< UInt32(plane + 1) << 16 {
                if let uniChar = UnicodeScalar(unicode), self.contains(uniChar) {
                    result.append(Character(uniChar))
                }
            }
        }
        return result
    }
}



print(CharacterSet.uppercaseLetters.description)
//<Foundation._SwiftNSCharacterSet: 0x6000000271a0>

print(String(CharacterSet.vowels.characters))
//AEIOUYaeiouy

print(CharacterSet.vowels.characters)
// ["A", "E", "I", "O", "U", "Y", "a", "e", "i", "o", "u", "y"]

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