Partial application of struct method is not allowed

gistfile1.swift

// Changing struct to class works swimmingly.
struct Test {
    func returnTwo() -> Int {
        return 2
    }

    func returnFive() -> Int {
        let twofunc = returnTwo  // Partial application of struct method is not allowed
        return twofunc() + 3
    }
}

let a = Test()
a.returnFive()