Swift Generics Issue

Swift generics issue: generic parameter could not be inferred

This is the wrong signature:

public func getLoginInfo(loginInfoClass: LoginInfoBase.Type, completionHandler: @escaping (Swift.Result<LoginInfoBase, Error>) -> Void)

You mean this:

public func getLoginInfo<T: LoginInfoBase>(loginInfoClass: T.Type, completionHandler: @escaping (Swift.Result<LoginInfoBase, Error>) -> Void)
                        ^^^^^^^^^^^^^^^^^^                 ^

You need to pass a concrete type to getLoginInfo that conforms to LoginInfoBase. Not just any subtype. This matches your genericQuery method.

You should then modify your call to genericQuery as:

genericQuery(urlString: "\(baseURL)/users/get_login_info/",
             method: .get,
             params: nil,
             decodable: T.self) { ... } // use T.self here.

For more details, see Alexander's link.

Swift Generics issue

With Swift, we'll need to think whether there's a function that can do the trick -- outside the methods of a class.

Just like in our case here:

contains(theArray, theItem)

You can try it in a playground:

let a = [1, 2, 3, 4, 5]
contains(a, 3)
contains(a, 6)

I discover a lot of these functions by cmd-clicking on a Swift symbol (example: Array) and then by looking around in that file (which seems to be the global file containing all declarations for Swift general classes and functions).

Here's a little extension that will add the "contains" method to all arrays:

extension Array {
    func contains<T: Equatable>(item: T) -> Bool {
        for i in self {
            if item == (i as T) { return true }
        }
        return false
    }
}

Swift generics and protocols issue

Sad to say, Swift doesn't perform implicit casting like that. As of now, you have to re-Box() the value.

func fetchComicsViewModel() -> Box<ComicViewModel> {
    return Box(sampleComics().value)
}

A type mismatch issue with generic methods

Is this what you wanted ?

struct One: Codable {}
struct Two: Codable {}

func test(ofType: Codable.Type) {
    print(ofType)
}

var array = Array<Codable.Type>()

array.append(One.self)
array.append(Two.self)

array.forEach { (type) in
    print(type)
} // Outs: One\nTwo

test(ofType: One.self) // out: One
test(ofType: Two.self) // out: Two

array.forEach { (type) in
    test(ofType: type)
} // Outs: One\nTwo

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