saoudrizwan

linesConvergingAnimation.isReversed = true
// Finish animation in reverse
linesConvergingAnimation.startAnimation()

saoudrizwan

linesConvergingAnimation = UIViewPropertyAnimator(duration: 0.2, curve: UIViewAnimationCurve.linear, animations: {
    // Set the new constraints
    self.firstLine.snp.remakeConstraints({ (make) in
        make.height.equalTo(self.lineHeight) // constant
        make.width.equalTo(self.containerView.snp.width)
        make.centerX.equalTo(self.containerView.snp.centerX)
        make.centerY.equalTo(self.containerView.snp.centerY)
    })
    self.thirdLine.snp.remakeConstraints({ (make) in
        make.height.equalTo(self.lineHeight) // constant

saoudrizwan

// Add a completion block to the UIViewPropertyAnimator 
linesConvergingAnimation.addCompletion({ (position) in
    // since this is the reversed animation's completion block, the
    // "final position" is the initial animation's target-start-position.
    if position == .start {
        self.linesAreX = false
        // reset constraints back to normal  
        self.firstLine.snp.remakeConstraints({ (make) in
            make.height.equalTo(self.lineHeight)
            make.width.equalTo(self.containerView.snp.width)

saoudrizwan

// show a nav bar
// 1. change some constraints
navBarHeightConstraint.update(offset: 80)
// 2. animate 
UIView.animate(withDuration: 0.10, delay: 0.0, options: .curveLinear, animations: {
  self.view.layoutIfNeeded() // Apple docs: "layout the subviews immediately"
}, completion: nil)

saoudrizwan

// 1. change some constraints
navBarHeightConstraint.update(offset: 80)
// 2. animate 
UIView.animate(withDuration: 0.10, delay: 0.0, options: .curveLinear, animations: {
  self.navBar.layoutIfNeeded()
}, completion: nil)

saoudrizwan

let numbers = [1, 2, 3, 4, 5]
var evenNumbers = [Int]()

for i in 0..<numbers.count {
    let number = numbers[i]
    if number % 2 == 0 {
        evenNumbers.append(number)
    }
}

saoudrizwan

/// Returns an array containing, in order, the elements of the sequence
/// that satisfy the given predicate.
/// - Parameter shouldInclude: A closure that takes an element of the
///   sequence as its argument and returns a Boolean value indicating
///   whether the element should be included in the returned array.
/// - Returns: An array of the elements that `includeElement` allowed.
public func filter(_ isIncluded: (Element) throws -> Bool) rethrows -> [Element]

saoudrizwan

let numbers = [1, 2, 3, 4, 5].map { $0 * 2 }
print(numbers) // [2, 4, 6, 8, 10]

saoudrizwan

let arrayWithNoNils = [1, 2, 3, nil].flatMap { $0 }
print(arrayWithNoNils) // [1, 2, 3]

saoudrizwan

let arrayWithNoOptionals = ["1", "two", "3"].flatMap { Int($0) }
print(arrayWithNoOptionals) // [1, 3]