Multiple protocol conformance build error workaround?

Question

Beast OP

Created Nov ’16

Replies 1

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Hello,

I'm getting a build error and wonder if there is a way to get multiple protocol conformance working.

protocol ProtocolA {}
protocol ProtocolB {}

protocol Protocol1 {
     var manager: ProtocolA?
}


protocol Protocol2 {
     var manager: ProtocolB?
}


class Implementation: Protocol1, Protocol2 {
     var manager: protocol<ProtocolA, ProtocolB>?
}

I get the following errors:
error: type 'Implementation' does not conform to protocol 'Protocol1'

error: type 'Implementation' does not conform to protocol 'Protocol2'

note: candidate has non-matching type '(ProtocolA & ProtocolB)?'

I would have thought that the compiler would have allowed Implementation's manager to conform to both protocols.

Any ideas on how to get something like this working?

Boost

Answer 1

ahltorp OP

Nov ’16

You want Implementation to conform to Protocol1. That means that this code should be valid:

class Foo: ProtocolA {}
var proto1instance = Implementation() as Protocol1
proto1instance.manager = Foo()

Since proto1instance is Protocol1, the compiler has no way of knowing that manager should also conform to ProtocolB.

But your code presumes that the compiler knows this. "class Implementation: Protocol1, Protocol2" means that the class should be able to appear as either Prococol1 and Protocol2, independently.

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