swift multi protocol error

demo.swift

/*

compilation error:

Type 'StructC' does not conform to protocol 'ProtoA'
Type 'StructC' does not conform to protocol 'ProtoB'

*/

protocol ProtoAInput {
    func funcA()
}

protocol ProtoA {
    var input: ProtoAInput { get }
}

protocol ProtoBInput {
    func funcB()
}

protocol ProtoB {
    var input: ProtoBInput { get }
}

struct StructC: ProtoA, ProtoB {
    var input: ProtoAInput & ProtoBInput { return self }
}

extension StructC: ProtoAInput {
    func funcA() { print("funcA") }
}

extension StructC: ProtoBInput {
    func funcB() { print("funcB") }
}

let s = StructC()
s.funcA()
s.funcB()