swift - 是否可以在 Swift 中编写一个失败的字符串编写器？

Question

如果我有这段代码:

let a : Int? = 10;
let b : String? = "Apples";
let result = "We have \(a) of \(b)";
// result will be "We have Optional(10) of Optional(Apples)"

我可以通过添加默认值来删除可选项:

let result = "We have \(a ?? 0) of \(b ?? "")";
// result will be "We have 10 of Apples"

但是，如果我希望如果字符串中的任何可选项为 nil，那么字符串结果完全为 nil 怎么办？

let a : Int? = nil;
let b : String? = "Apples";
let result = "We have \(a) of \(b)";
// result will be nil

所以我可以这样写:

let a : Int? = nil;
let b : String? = "Apples";
if let result = "We have \(a) of \(b)" { self.process(result); }

编辑:

我实际上想要实现的是这样的:

func process (_ s: String?) {
    guard let s = s else { return; }
    print (s);
}

let a : Int? = nil;
let b : String? = "Apples";
let result = "We have \(a) of \(b)";
self.process (result);

谢谢。

Answer 1

您可以使用 map/flatMap 可选的方法:

let a : Int? = nil
let b : String? = "Apples"

let result = a.flatMap { a in b.map { b in
    "We have \(a) of \(b)"
} }

结果是一个(常量)String?。如果 a 或 b 中的任何一个为 nil，则为 nil，否则为具有展开值的字符串。