fp-immutability

Immutability Principles

Immutability is a cornerstone of functional programming where data cannot be modified after creation. Instead of changing existing values, you create new values. This approach eliminates entire classes of bugs related to shared mutable state, makes code easier to reason about, and enables safe concurrent programming.

Core Concepts of Immutability

Immutable data has several key benefits:

1. Predictability: Data doesn't change unexpectedly
2. Thread Safety: No race conditions with immutable data
3. Easier Debugging: State changes are explicit and traceable
4. Temporal Logic: Can keep historical versions of data
5. Caching: Safe to cache references to immutable data

JavaScript: Immutability Patterns

// MUTABLE APPROACH (avoid)
const user = {
  name: 'Alice',
  email: '[email protected]',
  addresses: []
};

function addAddress(user, address) {
  user.addresses.push(address);  // Mutation!
  return user;
}

// IMMUTABLE APPROACH (prefer)
const userImmutable = {
  name: 'Alice',
  email: '[email protected]',
  addresses: []
};

function addAddressImmutable(user, address) {
  return {
    ...user,
    addresses: [...user.addresses, address]
  };
}

// Usage
const user1 = { name: 'Bob', addresses: [] };
const user2 = addAddressImmutable(user1, '123 Main St');

console.log(user1.addresses.length);  // 0 - unchanged
console.log(user2.addresses.length);  // 1 - new object

// Updating nested structures
const state = {
  user: {
    profile: {
      name: 'Charlie',
      settings: {
        theme: 'dark',
        notifications: true
      }
    }
  }
};

// MUTABLE (avoid)
function toggleNotificationsMutable(state) {
  state.user.profile.settings.notifications = !state.user.profile.settings.notifications;
  return state;
}

// IMMUTABLE (prefer)
function toggleNotificationsImmutable(state) {
  return {
    ...state,
    user: {
      ...state.user,
      profile: {
        ...state.user.profile,
        settings: {
          ...state.user.profile.settings,
          notifications: !state.user.profile.settings.notifications
        }
      }
    }
  };
}

// Using Immer library for simpler deep updates
import { produce } from 'immer';

function toggleNotificationsImmer(state) {
  return produce(state, draft => {
    draft.user.profile.settings.notifications = !draft.user.profile.settings.notifications;
  });
}