How are the properties of immutability related to the concept of function purity?

Immutability means that data does not change after creation. The property of immutability is closely related to the concept of pure functions, as a pure function should not modify external states and always returns the same result for the same inputs.

If a function works with immutable data, it does not modify it but creates new objects when necessary. This helps avoid side effects and makes the function predictable and reliable.

For example, in PHP, if a function takes an array and does not modify it but returns a new array with changes, it maintains immutability and is considered cleaner.