Chain blocks for asynchronous, callback-based execution. Always ends in main queue.

BlockChaining.swift

operator infix ~> { associativity right }
@infix func ~>(firstBlock: (() -> Void), secondBlock: (() -> Void)) -> (() -> Void) {
    return {
        dispatch_async(dispatch_get_global_queue(-32768, 0), {
            firstBlock()
            dispatch_async(dispatch_get_main_queue(), secondBlock)
        })
    }
}

// ...

({
    println(NSThread.currentThread()) // <NSThread: 0xb508c80>{number = 2, name = (null)}
} ~> {
    println(NSThread.currentThread()) // <NSThread: 0xb507b60>{number = 3, name = (null)}
} ~> {
    println(NSThread.currentThread()) // <NSThread: 0xb214a70>{number = 1, name = main}
})()