Generic in subscript for swift

Question

I understand that with Swift you can specify a function-specific generic with this form:

func someFunction<T>(type: T.Type) {...}

However, is it possible to do something similar with subscripts? Where you can specify a type within the brackets like so:

subscript<T>(type: T.Type) -> T {...}

EDIT: Updated solution based upon the accepted answer

subscript(type: AnyClass.Type) -> Any {
    return sizeof(type)
}

EDIT 2: Upon testing, It seems that I cannot actually use this subscript. I get "CLASS is not identical to AnyClass.Type" so I am back to square one

Answer 1

You can't define a subscript as a generic function, but you can use a generic type if it's declared at the class level.

For instance, lets say you want to make a class where the subscript takes a type T and returns a type U. That would look something like:

class SomeClass<T, U> {
    subscript(someParameter: T) -> U {
        /* something that returns U */
    }
}

For example, you could create a Converter class that used the subscript function to convert from type T to type U:

Note: This is a very contrived example, I wouldn't normally do this this way.

class Converter<T, U> {
    var _converter: (T -> U)

    init(converter: (T -> U)) {
        _converter = converter
    }

    subscript(input: T) -> U {
        let output = _converter(input)
        return output
    }
}

var convert = Converter(converter: {
    (input: Int) -> String in
    return "The number is: \(input)"
})

let s = convert[1]
println(s) // The number is: 1

Answer 2

Generic subscripts are now available in Swift 4: SE-0148