Here's a cool function that combines a value with a function to return a closure that captures that value, so that it can be called without any arguments. Super useful when working with closure-based APIs and we want to use some of our properties without having to capture self.

func combine<A, B>(_ value: A, with closure: @escaping (A) -> B) -> () -> B {
    return { closure(value) }
}

// BEFORE:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = { [weak self] in
            guard let self = self else {
                return
            }
            
            self.productManager.startCheckout(for: self.product)
        }
    }
}

// AFTER:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = combine(product, with: productManager.startCheckout)
    }
}