あるProtocolに定義されているComputed Propertyの値をそのProtocolに準拠したクラスのextension毎に違う値にする...?

Example.swift

protocol PhoneType{
    var number:String { get }
    func callTo(number:String)
}

extension PhoneType {
    func callTo(number:String) {
        print("Call to \(number) from \(self.number)")
    }
}

// MARK: - Phone

class Phone {
    func emergency() {
        CallManager.callToEmergency(self)
    }
}

/* "Protocolに準拠したクラスのextension" */
extension Phone: PhoneType {
    var number:String { return "111-xxx-xxx" }
}


// MARK: - Phone

/* Protocolに準拠したクラス */
class iPhone: PhoneType {
    func emergency() {
        CallManager.callToEmergency(self)
    }
    func heySiri() {
        CallManager.requestToSiriWith(self)
    }
}

/* のextension */
extension iPhone {
    var number:String { return "222-xxx-xxx" }
}

// MARK: - Manager

class CallManager {
    
    static func callToEmergency(phone:PhoneType) {
        phone.callTo("119")
    }
    
    static func requestToSiriWith<T:PhoneType where T:iPhone>(phone:T) {
        print("Accept your request :)")
    }
    
}

// MARK: - Try

CallManager.callToEmergency(Phone()) // Call to 119 from 111-xxx-xxx
CallManager.callToEmergency(iPhone()) // Call to 119 from 222-xxx-xxx