Question

swift新手，并尝试使用字符串插值打印Optional。我希望它在nil为空时打印Optional，但也希望它在实际包含字符串/字符时正确打印它。

所以我想要完成的工作应该可以在这里使用：

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

结果是值得结果或打印nil。

我该怎么做？我不想强行打开，因为我期待一些实际函数的测试返回nil。

对于记录，功能是：

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
}

我正试图打印：

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

Answer 1

这是功能：

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
    }

并致电：

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

输出控制台：

结果是：我

或

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

Answer 2

Swift 4

将字符可选或展开为字符串nil

let result = firstNonRepeatingCharacter(input: firstString)?.description ?? "nil"

print("\(firstString) should return \(result)")

Swift字符串/字符可选打印没有“可选”

2 个答案: