swift无法将类型“ [Liquor]”的值转换为预期的参数类型“ inout _”

Question

I go through some similar questions but still cannot figure out why this happen.

var liquors = [Liquor]()

func loadSampleLiquors(){
    let photo1 = UIImage(named: "Chateau Lafite Rothschild 1993")
    let liquor1 = Liquor(name: "Chateau Lafite Rothschild", year: "1993", photo: photo1, rating: 7)
    liquors += [liquor1] // Here is the error happen     
}

the error messageis : Cannot convert value of type '[Liquor]' to expected argument type 'inout _'

This is probably because the "year" may be nil, but I go through my code that it should work well, I try to fix it using "if let liquors = xxx", but then there will be a EXC_BAD_INSTRUCTION on the decode function, So I post all my code under here:

here is my liquor class:

var name: String
var year: String
var photo: UIImage?
var rating: Int

struct PropertyKey {
    static let nameKey = "name"
    static let yearKey = "year"
    static let photoKey = "photo"
    static let ratingKey = "rating"
}

I use NSCoding to store data:

func encode(with aCoder: NSCoder) {
    aCoder.encode(name, forKey: PropertyKey.nameKey)
    aCoder.encode(year, forKey: PropertyKey.yearKey)
    aCoder.encode(photo, forKey: PropertyKey.photoKey)
    aCoder.encode(rating, forKey: PropertyKey.ratingKey)
}

required convenience init?(coder aDecoder: NSCoder) {
    let name = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
    let year = aDecoder.decodeObject(forKey: PropertyKey.yearKey) as! String
    let photo = aDecoder.decodeObject(forKey: PropertyKey.photoKey) as? UIImage
    let rating = aDecoder.decodeInteger(forKey: PropertyKey.ratingKey)
    self.init(name: name, year:year, photo: photo, rating: rating)
}

Answer 1

You're missing the unwrap operator. Try this:

let liquor1 = Liquor(name: "Chateau Lafite Rothschild", year: "1993", photo: photo1, rating: 7)!

notice the "!" at the end

The reason you need to unwrap is because Liquor init can return nil, so it returns an optional. Thats the ? at the end of init

required convenience init?