Code Explainers

Code explainers tagged #immutability

ruby 
class Order
  class InvalidTransition < StandardError; end
 
  TRANSITIONS = {

A state machine for order transitions in Ruby

state-machine data-driven error-handling
Intermediate 8 steps
java 
public record FixedWidthField(String name, int start, int end) {
 
    public String extract(String line) {
        int from = Math.min(start, line.length());

Parsing fixed-width text in Java

records parsing streams
Intermediate 7 steps
php 
<?php
 
declare(strict_types=1);
 

An immutable typed collection in PHP

immutability value-objects iterators
Intermediate 8 steps
java 
package com.example.web.convert;
 
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

A custom ISO-week Converter in Spring

type conversion value object immutability
Intermediate 5 steps
typescript 
type EditorState = {
  content: string;
  cursor: number;
};

Undo/redo with two stacks in TypeScript

undo-redo stacks state-management
Intermediate 7 steps
javascript 
import { createContext, useContext, useReducer } from 'react';
 
const CartContext = createContext(null);
 

Building a shopping cart with Context in React

state management reducer context
Intermediate 10 steps
python 
import os
from dataclasses import dataclass
from functools import lru_cache
 

Loading typed config from environment variables

configuration environment-variables type-coercion
Intermediate 6 steps
php 
final class ConfigResolver
{
    private array $merged;
 

Layered config merging in PHP

recursion immutability variadics
Intermediate 8 steps
typescript 
type Change =
  | { kind: "added"; path: string; value: unknown }
  | { kind: "removed"; path: string; value: unknown }
  | { kind: "updated"; path: string; from: unknown; to: unknown };

Building a recursive deep-diff in TypeScript

recursion discriminated-unions type-guards
Intermediate 9 steps
java 
public final class ShippingAddress {
    private final String recipient;
    private final String line1;
    private final String line2;

Building immutable objects with the Builder pattern

builder-pattern immutability validation
Intermediate 7 steps
java 
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

Converting timestamps across time zones in Java

date-time time-zones instant
Intermediate 6 steps
typescript 
import { Injectable, Scope, Inject } from '@nestjs/common';
import { REQUEST } from '@nestjs/core';
import { Request } from 'express';
 

Request-scoped context service in NestJS

dependency-injection request-scope immutability
Intermediate 8 steps
java 
public class OrderSerializer {
 
    private final ObjectMapper mapper;
 

Configuring a reusable Jackson ObjectMapper

serialization json builder-pattern
Intermediate 8 steps
ruby 
module ConfigMerge
  module_function
 
  def deep_merge(base, override)

Recursively merging nested config hashes in Ruby

recursion hash-merge immutability
Intermediate 8 steps
ruby 
module DeepFreeze
  module_function
 
  def call(obj)

Recursively freezing nested Ruby data

recursion immutability pattern matching
Intermediate 9 steps
java 
public record ServerConfig(String host, int port, boolean tls, List<String> allowedOrigins) {
 
    public ServerConfig {
        Objects.requireNonNull(host, "host is required");

Validating config with a Java record

records validation immutability
Intermediate 9 steps
javascript 
export function cloneState(state) {
  if (typeof structuredClone !== "function") {
    throw new Error("structuredClone is not available in this runtime");
  }

Deep cloning with structuredClone

deep-copy error-handling immutability
Intermediate 7 steps
java 
package com.example.billing;
 
import java.math.BigDecimal;
import java.math.RoundingMode;

Locale-aware currency formatting in Java

internationalization rounding immutability
Intermediate 6 steps