Swift可选赋值，处理nil/空字符串

Question

我正在尝试解决 Swift 中的字符串分配问题:这里我们有一个结构:

struct Student {
    var name: String
    var id: String
    var mentor: String?
    var grade: String?
}

我们想把它解析成一个字符串，像这样:

if (mentor != nil && grade != nil) {
    return "Student info: name:" + name + " id:" + id + " mentor:" + mentor! + " grade:" + grade! + "."
} else if (mentor != nil) {
    return "Student info: name:" + name + " id:" + id + " mentor:" + mentor! + "."
} else if (grade != nil) { 
    return "Student info: name:" + name + " id:" + id + " grade:" + grade! + "."
} else {
    return "Student info: name:" + name + " id:" + id + "."
}

我是Swift新手，上面的代码是基于其他语言的经验，请问在Swift中有没有更简洁的实现方式？就像处理可选的 toString() 一样，如果它是 nil 则返回一个空字符串 ""?

Answer 1

Alexander 的回答很好，并且很好地利用了高阶函数 map()，但如果您刚刚开始，这可能会让您有些不知所措。通过明智地使用 if let “optional binding”，您可以大大简化您的代码:

var result = "Student info: name:" + name + " id:" + id
if let mentor = mentor {
  result += " mentor:" + mentor
}
if let grade = grade {
  result += " grade:" + grade
}
result += "."

return result

或重写以避免 + 运算符:

var result = "Student info: name:\(name) id:\(id)"
if let mentor = mentor {
  result.append(" mentor:\(mentor)")
}
if let grade = grade {
  result.append(" grade:\(grade)")
}
result.append(".")

return result