Lab: The Mutating State

Welcome to the interactive lab on Immutability! We will explore this concept through a Problem-Based Learning (PBL) approach in three acts.

Act 1: The Hook

Imagine you are building a banking application. You have an account with a balance of $100. Two transactions happen at the exact same time: a deposit of$50 and a withdrawal of $20.

If both transactions read the balance as $100 before applying their changes, what could go wrong?

Act 2: Mental Model

In a world with mutable state, variables are like chalkboards. Anyone can erase the current value and write a new one. When multiple processes write to the same chalkboard concurrently, the final message becomes unpredictable.

Immutability, on the other hand, treats data as a historical ledger. Instead of erasing and rewriting, every change produces a brand new page with the updated information. The old page remains unchanged.

Act 3: The Rabbit Hole

Let us dive deeper. Consider how memory allocation works in programming languages when dealing with immutable data structures. Functional languages often use techniques like structural sharing to make immutability efficient.

When you modify an element in an immutable list, the language does not copy the entire list. Instead, it creates a new list that shares most of its structure with the original one.