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Mastering Swift 4 - Fourth Edition by Jon Hoffman

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Constants and variables

Constants and variables associate an identifier (such as myName or currentTemperature) with a value of a particular type (such as the String or Int type), where the identifier can be used to retrieve the value. The difference between a constant and a variable is that a variable can be updated or changed, while a constant cannot be changed once a value is assigned to it.

Constants are good for defining values that you know will never change, like the temperature that water freezes at or the speed of light. Constants are also good for defining a value that we use many times throughout our application, such as a standard font size or the maximum number of characters in a buffer. There will be numerous examples of constants ...

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