Can't dynamically check for fulfillment of type constraints

NoDynamicConstraint.swift

//: Playground - noun: a place where people can play

import Cocoa

let a: Int? = 3
let b: Int? = 3

public func equateThem <T: Equatable>(lhs : Optional<T>, rhs : Optional<T>) -> Bool {
    return lhs! == rhs!
}

func takeTwo<T>(a: Optional<T>, b: Optional<T>) {
    // no way to cast in a way to enforce same type requirement & Equatable
    // would need something like:   (if <T: Equatable> let a = as as? T, let b = as? T)
    equateThem(a, rhs: b)
}

takeTwo(a, b: b)