CODEWITHSUNDEEP
swiftgenericsprotocols
Mohmmad S
Mohmmad S

Reputation: 5098

Can you Strict Generic types or give one parameter more than one type ?

For example i want to specify a type that might be Integer or String and use it as special type in func i tried typealias but it wont solve the case because typealiases can't have or arguments as its only uses & therefore consider the case below. 

typealias alis = StringProtocol & Numeric


func foo <T: alis> (vee: T) -> T{
// do something
    return vee
}

i want this func to accept a parameter type of either ( Int or String ) not anything else (<T>),

as you can see i tried with typealias and i have no compile error.

however trying to use the function will lead to these errors. 

foo(vee: 1) //Argument type 'Int' does not conform to expected type 'StringProtocol'

And 

foo(vee: "v") //Argument type 'String' does not conform to expected type 'Numeric'

is this achievable with swift ? if so how.

Upvotes: 3

Views: 209

Answers (1)

Sweeper
Sweeper

Reputation: 273978

Let's suppose that you could use a OR operator to combine protocols, what would you be able to do with something of type (Int | String)?

Not everything you can do to an Int can be done on (Int | String), because it might be a string underlyingly. Similarly, not everything you can do to an String can be done on (Int | String), because it might be a Int underlyingly.

Now you might say "Ah. I know that Int and String both have a description property. I should be able to access description on a variable of type (Int | String)."

Well, in that case, you can just create such a protocol yourself and only have Int and String conform to it:

protocol IntOrString {
    var description: String { get }
}

extension Int : IntOrString {}
extension String : IntOrString {}

(Note that description is already defined in CustomStringConvertible. For the sake of argument, imagine that does not exist.)

Upvotes: 4

Related Questions