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Execute a method when a variable value changes in Swift

This post is about how to execute a function when a variable value changes.

Instead of key-value observation, simply use a property observer for the variable. 

For e.g:

Whenever the value of variable named allSlot changes, the two lines will execute which are written in the didSet method.
private var allSlot: [String] = [] {
        didSet {
            slotTableView?.reloadData()
            enableRightBarButton()
        }
    }

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