小编Ser*_*yev的帖子

在类似情况下，如何检查对象是否符合“可表示”协议？

protocol Representable {
    associatedtype RepresentType
    var representType: RepresentType { get set }
}

class A: UIView, Representable {
    enum RepresentType: String {
        case atype = "isa"
    }
    var representType: RepresentType = .atype
}

class B: UIView, Representable {
    enum RepresentType {
        case btype(value: String?)
    }
    var representType: RepresentType = .btype(value: nil)
}

let obj = A()
if let obj = obj as? Representable {  <<<<<<<<<<<< error
    obj.representType = A.RepresentType.atype
}

错误：协议 'Representable' 只能用作通用约束，因为如果 let obj = obj as? 具有代表性 …