Scala has a clear separation between mutable and immutable assignments. In Scala, values are immutable: you cannot modify them after creating them. Variables are mutable: they can refer to different instances over time. Deciding when to declare a value rather than a variable is essential for your code to be fast and bug-free. Variables are more straightforward to use in your code because you can modify them. However, they can make your program extremely difficult to maintain and lead to errors when different processes try to do so simultaneously. Values can be challenging to use because you cannot modify them once created. But they can make your program easier to understand: their assignments never change, so you can easily predict and test their evaluation. They also guarantee that your code will not be affected by concurrency issues, such as data inconsistencies, resources starvation, and deadlocks, when accessed by several threads. A fragment of code that multiple processes can access without causing concurrency issues is thread-safe. In the capstone for this unit, you’ll define both values and variables to name fragments of code and make your program more readable.
