ios - Extending Lists in Swift -

i'm developing backend part of system using apple's swift needs deal email lists (an array of email objects) , need set own properties list such allowrepeated: bool, , methods performcleanup() remove duplicate entries if allowrepeated property set true.

i have done in playground trying follow documentation notes extending nsmutablearray class:

class emaillist: nsmutablearray {     override var count: int {         {             // seems line below generates infinity loop             return nsarray(array: self).count         }     }      override func insertobject(anobject: anyobject, atindex index: int) {         insertobject(anobject, atindex: index)     }      override func removeobjectatindex(index: int) {         super.removeobjectatindex(index)     }      override func addobject(anobject: anyobject) {         super.addobject(anobject)     }      override func removelastobject() {         super.removelastobject()     }      override func replaceobjectatindex(index: int, withobject anobject: anyobject) {         super.replaceobjectatindex(index, withobject: anobject)     }      override func objectatindex(index: int) -> anyobject {         return super.objectatindex(index)     } } 

it seems line return nsarray(array: self).count causing infinite loop. why happening?

cocoa collection classes (such nsmutablearray) what's known "class clusters" , not meant subclassed. guarantee malfunctions due subclassing nsmutablearray.

in case, i'm guessing when strange count override tries create array own contents, it's once again asked count when array(array:) constructor called, since array(array:) presumably needs know how long it'll based on passed source array. lather, rinse, repeat.

the real question why short-circuit basic cocoa class in way? possible gains feel you're getting causing creation of whole new array when nsmutablearray.count works fine? don't things this.