编程初学者，学习swift中，官方教材这边要求创建一个新类Circle继承NamedShape,构造器接收两个参数,一个是半径一个是名称,在子类 Cir cle 中实现 area() 和 simpleDescription() 方法。
但是在playground中一直提示出错，undetermined string literal和invalid character in source file 还有 use of unresolved identifier 'littleCircle'

class NamedShape {

var numberOfSides: Int = 0
var name: String

init(name: String) {
    self.name = name
}

func simpleDescription() -> String {
    return "A shape with \(numberOfSides) sides."
}

}

class Circle:NamedShape{

    var halfLength:Double
    
    init (halfLength:Double,name:String){
        self.halfLength = halfLength
        super.init(name:name)
        numberOfSides = 4
    }
    
    func area() -> Double{
        return 3*halfLength*halfLength
    }
    
    override func simpleDescription()->String{
        return “A circle with halfLength of \(halfLength)"
    }
    

}

let test = Circle(halfLength: 2.0, name: littleCircle)