Capture.swift

import UIKit
import XCPlayground
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

func perform(initial: Int) {
    var value: Int = initial
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 1), dispatch_get_main_queue()) { [myConstant = value] in
        print("constant in first block \(myConstant)")
        print("captured \(value)")
        value = initial * 2
    }

    value = initial + 1

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2), dispatch_get_main_queue()) { [myConstant = value] in
        print("constant in second block \(myConstant)")
        print("captured \(value)")
    }
}

perform(10)

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 3), dispatch_get_main_queue()) {
    print("--------")
    perform(30)
}

// Console:
constant in first block 10
captured 11
constant in second block 11
captured 20
--------
constant in first block 30
captured 31
constant in second block 31
captured 60