AnyObject.property is slower than ActualClass.property

AnyObjVs.swift

import Foundation

@objc class MyClass: NSObject {
    var someProperty: Int
    init(_ x: Int) { someProperty = x }
}
let classes: [AnyObject] = (0..<10_000).map { _ in MyClass(Int(arc4random())) }

func timeRun<T>(name: String, f: ()->T) -> String {
    let start = CFAbsoluteTimeGetCurrent()
    let result = f()
    let end = CFAbsoluteTimeGetCurrent()
    let timeStr = toString(Int((end - start) * 1_000_000))
    return "\(name)\t\(timeStr)µs, produced \(result)"
}

let runs = [
    ("Using AnyObj.someProperty", {
        reduce(classes, 0) { prev,next in max(prev,next.someProperty) }
    }),
    ("Using MyClass.someProperty", {
        reduce(classes, 0) { prev,next in
            (next as? MyClass).map { max(prev,$0.someProperty) } ?? prev
        }
    }),
    ("Using plain ol' for loop", {
        var maxSoFar = 0
        for obj in classes {
            if let mc = obj as? MyClass {
                maxSoFar = max(maxSoFar, mc.someProperty)
            }
        }
        return maxSoFar
    }),
]

println("\n".join(map(runs, timeRun)))

SampleOutput

With optimization:   (swiftc -O AnyObjVs.swift)

Using AnyObj.someProperty               3365µs, produced 4294759641
Using MyClass.someProperty              1189µs, produced 4294759641
Using plain ol' for loop                1197µs, produced 4294759641

Without:             (swiftc -Onone AnyObjVs.swift)

Using AnyObj.someProperty              10944µs, produced 4294758501
Using MyClass.someProperty             13944µs, produced 4294758501
Using plain ol' for loop                8189µs, produced 4294758501