Swift 错误：无法将“字符”类型的值转换为预期的参数类型“Unicode.Scalar”

Question

I'm new to Swift and having problems with this function below. I'm Using SWIFT 5/Xcode 11.3. The function is designed to remove any letters prior to a vowel. For instance, "Brian" would return "ian", "Bill" would return "ill", etc. I'm getting the errors on the 2 lines below.

import Foundation

func shortNameFromName(_ name: String) -> String {

    // Definition of characters
    let vowels = CharacterSet(charactersIn: "aeiou")
    var shortName = ""
    let start = name.startIndex

    // Loop through each character in name
    for number in 0..<name.count {

        // If the character is a vowel, remove all characters before current index position
        if vowels.contains(name[name.index(start, offsetBy: number)]) == true { //**ERROR: Cannot convert value of type 'Character' to expected argument type 'Unicode.Scalar'**
            var shortName = name.remove(at: shortName.index(before: shortName.number)) //**ERROR: Cannot use mutating member on immutable value: 'name' is a 'let' constant**
        }
    }

    //convert returned value to lowercase
    return name.lowercased()
}

var str = "Brian" // Expected result is "ian"

shortNameFromName(str)

Answer 1

You can use collection's method func drop(while predicate: (Character) throws -> Bool) rethrows -> Substring while the string "aeiou" does not contain character and return a Substring:

func shortName(from name: String) -> String { name.drop{ !"aeiou".contains($0) }.lowercased() }

shortName(from: "Brian")  // "ian"    
shortName(from: "Bill")   // "ill"

Regarding the issues in your code check the comments through the code bellow:

func shortName(from name: String) -> String {
    // you can use a string instead of a CharacterSet to fix your first error
    let vowels =  "aeiou"
    // to fix your second error you can create a variable from your first parameter name
    var name = name
    // you can iterate through each character using `for character in name`
    for character in name {
        // check if the string with the vowels contain the current character
        if vowels.contains(character) {
            // and remove the first character from your name using `removeFirst` method
            name.removeFirst()
        }
    }
    // return the resulting name lowercased
    return name.lowercased()
} 

shortName(from: "Brian")  // "ian"