swift - 从方法返回可选值

Question

我有一组基本的结构，包括定义车库的 Garage 结构、封装硬编码车库列表的 Garages 类，以及 >Car 类，根据制造商字符串搜索车库。

我的问题是 Car.findGarageByManufacturer 需要有选择地返回一个 Garage 实例(如果找不到则返回 nil)。` 但是我收到以下错误:

可选类型“车库”的值？未展开；你是不是想用'!'或者 '？' ?

...在线return foundGarage

如何在方法内部返回可选值？

// Using a struct because an 'Object' type doesn't seem to exist :-/
struct Garage {
    var name: String
    var manu: String
}

// Hardcorded set of garages, using class to test returning an array of a struct instance.
class Garages {
    func getGarages() -> Array<Garage> {
        var garages: Garage[] = [
            Garage(name: "VW Car Park", manu: "VW"),
            Garage(name: "Williams BMW", manu: "BMW"),
            Garage(name: "Hadwins", manu: "VW")
        ]
        return garages;
    }
}

// Immediately create an instance of the Garages class
let garages = Garages()

class Car {
    func findGarageByManufacturer(manufacturer: String) -> Garage {
        var foundGarage: Garage? = nil
        for garage in garages.getGarages() {
            if(garage.manu == manufacturer) {
                foundGarage = garage
            }
        }
        // This is the line that's causing an error
        // How do we optionally return a garage?
        return foundGarage
    }
}

Answer 1

func findGarageByManufacturer(manufacturer: String) -> Garage

必须是

func findGarageByManufacturer(manufacturer: String) -> Garage?

(注意问号)