A more generic approach to expectations

GenericMatchers.swift

import Cocoa

protocol Matcher {
  typealias Matchable
  func matches(object: Matchable) -> Bool
}

class EqualMatcher<T:Equatable>: Matcher {
  typealias Matchable = T
  
  // this is a workaround for non-fixed class layout issues
  let backingVar: T[]
  
  var object: T {
    get {
      return backingVar[0]
    }
    set {
      backingVar[0] = newValue
    }
  }
  
  init(_ object: T) {
    self.backingVar = [object]
  }
  
  func matches(otherObject: T) -> Bool  {
    return object == otherObject
  }
}

class GreaterThanMatcher<T: Comparable>: Matcher {
  typealias Matchable = T
  
  // this is a workaround for non-fixed class layout issues
  let backingVar: T[]
  
  var object: T {
    get {
      return backingVar[0]
    }
    set {
      backingVar[0] = newValue
    }
  }
  
  init(_ object: T) {
    self.backingVar = [object]
  }
  
  func matches(otherObject: T) -> Bool  {
    return otherObject > object
  }
}

class Expectation<T> {
  // this is a workaround for non-fixed class layout issues
  let backingVar: T[]
  
  var object: T {
    get {
        return backingVar[0]
    }
    set {
        backingVar[0] = newValue
    }
  }
  
  init(_ object: T) {
    self.backingVar = [object]
  }
  
  func to<M: Matcher where M.Matchable == T>(matcher: M) -> Bool {
    return matcher.matches(object)
  }
  
  func notTo<M: Matcher where M.Matchable == T>(matcher: M) -> Bool {
    return !to(matcher)
  }
}

func expect<T>(object: T) -> Expectation<T> {
  return Expectation(object)
}

func equal<T:Comparable>(object: T) -> EqualMatcher<T> {
  return EqualMatcher(object)
}

func beGreaterThan<T: Comparable>(object: T) -> GreaterThanMatcher<T> {
  return GreaterThanMatcher(object)
}

expect(123).to(equal(123))
expect(123).notTo(equal(456))
expect(100).to(beGreaterThan(50))

I struggled to get the proxy/operator styles working with this so if anybody can figure out that would be great! You can see the proxy implementation here:

https://gist.github.com/lukeredpath/6af2f55f65faa52de74d