Swift Protocol inheritance and protocol conformance issue -

protocol basepresenterprotocol : class {} protocol dashboardpresenterprotocol : basepresenterprotocol {}  final class dashboardpresenter {     weak var view: dashboardpresenterprotocol?      init() {         self.view = dashboardviewcontroller()     }      func test() {         print("hello")     } }  extension dashboardpresenter: dashboardviewprotocol { }  protocol baseviewprotocol : class {     weak var view: basepresenterprotocol? { set } }  protocol dashboardviewprotocol : baseviewprotocol { }  class dashboardviewcontroller { }  extension dashboardviewcontroller: dashboardpresenterprotocol { } 

in above code, error @ following line

extension dashboardpresenter: dashboardviewprotocol { } 

that, dashboardpresenter doesn't confirm protocol dashboardviewprotocol, have declared weak var view: dashboardpresenterprotocol? in dashboardpresenter . although have declared

why getting error ? please let me know doing wrong in code.

you cannot implement read-write property requirement of type basepresenterprotocol? property of type dashboardpresenterprotocol?.

think happen if were possible, , upcast instance of dashboardpresenter dashboardviewprotocol. able assign conforms basepresenterprotocol property of type dashboardpresenterprotocol? – illegal.

for reason, read-write property requirement has invariant (although it's worth noting readable-only property requirement should able covariant – but isn't supported).

although in case, protocols don't conform themselves, cannot use dashboardpresenterprotocol? type conforms basepresenterprotocol?.