CODEWITHSUNDEEP
swiftprotocols
Crocobag
Crocobag

Reputation: 2340

Restriction on associatedtype to an Array

I have a protocol with an associatedtype and I made some of my classes conform to it:

protocol MyProtocol {
    associatedtype MyType
    func myFunction()-> MyType
}

struct MyStruct: Codable {
    var myVar: Int
}

class MyClass1: MyProtocol {
    func myFunction()-> [MyStruct]? {
        return [MyStruct(myVar: 1)]
    }
}

class MyClass2: MyProtocol {
    func myFunction()-> Int? {
        return 1
    }
}

Now I want to create a protocol that can only be applied to an object that is conform to MyProtocol and its associatedtype is an array of Codable like so:

protocol MyProtocolCodable where Self: MyProtocol, MyType: [Codable] {} 🛑

However I get an error:

Type 'Self.MyType' constrained to non-protocol, non-class type '[Codable]' (aka 'Array<Decodable & Encodable>')

How can I get around this problem and apply my restriction?

Note: I get the same error when trying to restrict with any kind of Array, but works fine with other types:

protocol MyProtocolCodable where Self: MyProtocol, MyType: [Int] {} 🛑
protocol MyProtocolCodable where Self: MyProtocol, MyType: Array<Any> {} 🛑

Upvotes: 2

Views: 149

Answers (2)

ZeroOnet
ZeroOnet

Reputation: 15

You should use '==' to make associatedType constraints, replace yours instead of:

protocol MyProtocolCodable where Self: MyProtocol, MyType == [Codable] {}

Upvotes: 0

pawello2222
pawello2222

Reputation: 54436

This is because Array is not a protocol, it's a struct:

@frozen struct Array<Element>

You can try to conform to Sequence instead:

protocol MyProtocolCodable where Self: MyProtocol, MyType: Sequence, MyType.Element: Codable {}

Upvotes: 4

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