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swiftgeneric-programming

Multiple constraints on parameter of a generic function

Reading about generic functions in Swift, I see that it is possible to put some constraints on a parameter by requiring, that it is a subclass of a given class C, or that it implements a given protocol P. But I wonder if there is a way to require both at the same time. I haven't found anything about that yet.

Does anyone know?

Solution

  • Actually You can do that.

    If you have seen Codable in swift it is actually Decodable and Encodable

     typealias Codable = Decodable & Encodable

    So in some function if you are using generic T as Codable 

    struct StructOfCodable<T:Codable>: Codable {
     ....
}

    Here is example 

    protocol Test {}
class TClass {

}

typealias Common = Test & TClass

func generic <T:Common>(method:T) {

}

    Another way is protocol and class both can have super class. So you can create common protocol

    like 

    protocol CommonInProtocolAndStruct { }

protocol ProtocolUsedAsConstraint:CommonInProtocolAndStruct {} 

struct StructUsedAsConstraint:CommonInProtocolAndStruct {}

    And any method you can use CommonInProtocolAndStruct as generic constraint