swift set intersect, union, subtract
<p>Does anyone know how to implement set operations with user defined classes, with its property as operated conditions. For instance: </p>

<pre><code>class myClass {
  var figure: Int!
} 

let classObj1 = myClass() 
classObj1.figure = 1

let classObj2 = myClass()
classObj2.figure = 2

let classObj3 = myClass()
classObj3.figure = 1

let set1: Set = [classObj1]
let set2: Set = [classObj2, classObj3]
</code></pre>

<p>Is there any method like: (pseudo code)</p>

<pre><code>set2.substract(set1) {s2, s1 in s2.figure == s1.figure}
</code></pre>

<p>...so the expected result is <code>[classObj2]</code>?</p>

<p>Many thanks for any suggestion!</p>