Notes from Capturing Values In Swift Closures

Within a closure, referring to variables outside of the closure, strong references are created.

class MyClass {
    let a = 1
    let myClosure = {
        print(self.a)
    }
    myClosure() // 1
    a = 2
    myClosure() // 2
}

If we don’t want the strong ref, we can specify weak



class MyClass {
    let a = 1
    let myClosure = { [weak self] in
        guard let strongSelf = self else { return }
        print(strongSelf.a)
    }
    myClosure() // 1
    a = 2
    myClosure() // 1    <-- here's the difference
}

Nice article says it all.

class MySingleton {
    static let sharedInstance = MySingleton()
    private init() {}
}

Why? Scaling images on the fly impact performance.
How? If you have no control over the incoming image size, then scale the image outside of the main thread before displaying.

What? A queue that runs tasks FIFO.

Types? 

• Serial – one at a time
• system-provided: main queue
• you can create your own
• Concurrent – 1+ tasks at a time
• system-provided: 4 queues (high, default, low, and background)
• you can create your own, but 4 system ones should be good enough