Immutable vs. Mutable Types in Programming: What's the Difference?

Immutable vs Mutable Types: Understanding the Difference

When working with data in programming, it's essential to understand the distinction between immutable and mutable types. Immutable types are objects whose value cannot be changed after they are created, while mutable types can be modified in place.

Understanding Immutable Types

As the example with the RoundFloat class illustrates, an immutable type is immutable because its class defines the __new__() method, which creates a new instance of the class without modifying the existing object. This ensures that any changes to the object's value are reflected in a new instance, leaving the original object unaltered.

Similarly, the SortedKeyDict class is considered immutable due to the use of __new__() in its constructor. It creates a new object by clearing the input dictionary, creating a new, sorted dictionary. This process leaves the original dictionary unchanged, preserving its immutability.

Characteristics of Mutable Types

Mutable types, on the other hand, have methods that can modify the object in place. This allows for altering the object's value without creating a new instance. For example, the SortedKeyDict_a class has an example method that modifies the object by extracting its keys.

The Case of Lists and Dictionaries

Sets, like lists, are mutable data structures as well. In contrast to strings, passing a set to the RoundFloat class with __new__() will not trigger an error because sets are mutable.

The situation with dictionaries is slightly different. While dictionaries are considered mutable by default, the SortedKeyDict class removes this mutability by using __new__() to clear the input dictionary and create a new, sorted one. This ensures that the original dictionary remains unaltered.

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