Passing a Swift protocol to an Objective-C pointer

Passing a Swift protocol to an Objective-C pointer

<em>Using XCode 10.1 / Swift 4.2.</em>

Using XCode 10.1 / Swift 4.2.

I'm trying to assign an object that conforms to a Swift protocol to an Objective-C pointer. The following code is a minimal example that compiles and works as expected, but it gives me the following warnings:

If assigning to a local variable: Incompatible pointer types initializing 'NSObject<Animal> *__strong' with an expression of type 'id<Animal> _Nullable'

If assigning to a stored property: Incompatible pointer types assigning to 'NSObject<Animal> *' from 'id<Animal> _Nullable'

Any idea on how to address that warning without just silencing it?

Swift code:

@objc protocol Animal {
    var name: String { get }

@objc class Pig: NSObject, Animal { var name: String = "pig" }

@objc class Cow: NSObject, Animal { var name: String = "cow" }

@objc class Farm: NSObject { static func getAnimal(name: String) -> Animal? { // return some animal or nil } }

Objective-C code:

// This code returns a valid pointer to a Pig object
// that is usable in objective-c, but it also triggers 
// the warning described above
NSObject<Animal>* animal = [Farm getAnimalWithName:@"pig"];

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