没有 "Optional"的 Swift 字符串/字符可选打印

Question

swift 的新手，并尝试打印带有字符串插值的 Optional。我希望它在 Optional 为空时打印 nil，但也希望它在实际包含字符串/字符时正确打印字符串/字符。

所以我想要完成的应该可以在这里使用:

print("The result is: \(funcToReturnOptional)")

结果是有值的结果或被打印的nil。

我该怎么做？我不想强制解包，因为我希望对实际函数进行一些测试以返回 nil。

为了记录，函数是:

func firstNonRepeatingChar(input:String)->Character?{
    //set a default return object
    var result: Character? = nil
    //convert input for easy and clean navigation
    let converted = Array(input)
    //set start of enumeration
    var index: Int = 0
    //set variable to compare
    var c:Character
    //should only trigger if non-empty input
    while index<converted.count-1{
        c=converted[index]
        //check for non-repeated value
        if !converted[index+1..<converted.count].contains(c){
            result=c
            return result
        }
        index+=1
    }
    return result
}

我正在尝试像这样打印:

print(firstString+" should return \(firstNonRepeatingCharacter(input: firstString)??"nil")")

Answer 1

这是函数:

func firstNonRepeatingChar(input:String)->Character?{
        //set a default return object
        var result: Character? = nil
        //convert input for easy and clean navigation
       // let converted = Array(input) swift2
        let converted = [Character](input.characters) //swift3
        //set start of enumeration
        var index: Int = 0
        //set variable to compare
        var c:Character
        //should only trigger if non-empty input
        while index<converted.count-1{
            c=converted[index]
            //check for non-repeated value
            if !converted[index+1..<converted.count].contains(c){
                result=c
                return result
            }
            index+=1
        }
        return result
    }

并调用:

print("The result is: \(firstNonRepeatingChar(input: "I miss you")?.description ?? "nil")")

输出控制台:

The result is: I

或

 let fistString = "I miss you"  
 print("here is FistString: \(fistString) and The result is: \(firstNonRepeatingChar(input: fistString)?.description ?? "nil")")