How do you create textfield padding in Swift 4?

As @the4kman says, Swift does support CGRect but the syntax may have changed.

You can try this for instance:

@IBOutlet weak var nameTextField: UITextField! {
    didSet {
        nameTextField.layer.cornerRadius =  5
        nameTextField.layer.borderColor = UIColor.black.cgColor
        nameTextField.layer.borderWidth = 1
        let leftView = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 100.0, height: 2.0))
        nameTextField.leftView = leftView
        nameTextField.leftViewMode = .always
    }
}

If I do that, I get this fine result

Hope that helps.

Update

You ask for a function instead of setting it in didSet and sure, thats possible, something like:

func addPaddingAndBorder(to textfield: UITextField) {
    textfield.layer.cornerRadius =  5
    textfield.layer.borderColor = UIColor.black.cgColor
    textfield.layer.borderWidth = 1
    let leftView = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 100.0, height: 2.0))
    textfield.leftView = leftView
    textfield.leftViewMode = .always
}

and then you' call that in viewDidLoad for instance like so:

override func viewDidLoad() {
    super.viewDidLoad()
    addPaddingAndBorder(to: nameTextField)
}

Better to subclass the textview than to add a left view incase you are planning to add an image as a left view.

class UITextFieldPadding: UITextField {

    let padding = UIEdgeInsets(top: 0, left: 40, bottom: 0, right: 0)

    override open func textRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }

    override open func placeholderRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }

    override open func editingRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }
}

Customized way to add padding in "left", "right" or "both" side od UITextField.

Step 1:- Add this UITextfield extension

extension UITextField {

    enum PaddingSide {
        case left(CGFloat)
        case right(CGFloat)
        case both(CGFloat)
    }

    func addPadding(_ padding: PaddingSide) {

        self.leftViewMode = .always
        self.layer.masksToBounds = true


        switch padding {

        case .left(let spacing):
            let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: spacing, height: self.frame.height))
            self.leftView = paddingView
            self.rightViewMode = .always

        case .right(let spacing):
            let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: spacing, height: self.frame.height))
            self.rightView = paddingView
            self.rightViewMode = .always

        case .both(let spacing):
            let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: spacing, height: self.frame.height))
            // left
            self.leftView = paddingView
            self.leftViewMode = .always
            // right
            self.rightView = paddingView
            self.rightViewMode = .always
        }
    }        
}

Step 2: How to use

// 1.  To add left padding
yourTextFieldName.addPadding(.left(20)) 

// 2.  To add right padding
yourTextFieldName.addPadding(.right(20))

// 3. To add left & right padding both
yourTextFieldName.addPadding(.both(20))