Code Explainers

Browse the library

java 
public final class CircuitBreaker {
 
    private enum State { CLOSED, OPEN, HALF_OPEN }
 

How a circuit breaker guards failing calls

state-machine resilience concurrency
Advanced 7 steps
php 
final class InvoiceCalculator
{
    private const SCALE = 4;
 

Precise money math with PHP's BCMath

bcmath arbitrary precision money
Intermediate 8 steps
python 
import re
from dataclasses import dataclass, field
 
 

Building a table of contents from Markdown

regular-expressions parsing slugification
Intermediate 9 steps
javascript 
const IBAN_LENGTHS = {
  DE: 22, FR: 27, GB: 22, ES: 24, IT: 27,
  NL: 18, BE: 16, CH: 21, AT: 20, PT: 25,
};

How IBAN validation works in JavaScript

validation checksum modular-arithmetic
Intermediate 8 steps
rust 
use std::collections::HashMap;
 
#[derive(Clone, Copy, PartialEq)]
enum Color {

Detecting cycles with three-color DFS in Rust

graph-algorithms cycle-detection depth-first-search
Intermediate 9 steps
typescript 
import { useCallback, useRef, useState } from "react";
 
type UploadZoneProps = {
  accept?: string[];

A drag-and-drop file upload zone in React

drag-and-drop file-validation controlled-state
Intermediate 9 steps
ruby 
class MailingListDeduplicator
  GMAIL_DOMAINS = %w[gmail.com googlemail.com].freeze
 
  def initialize(subscribers)

Deduplicating a mailing list by canonical email

deduplication normalization service object
Intermediate 8 steps
go 
package middleware
 
import (
	"fmt"

How a panic-recovery middleware works in Gin

middleware panic-recovery error-reporting
Intermediate 8 steps
java 
public Map<Long, CustomerDto> indexByCustomerId(List<CustomerDto> customers) {
    return customers.stream()
            .collect(Collectors.toMap(
                    CustomerDto::getId,

Building maps from lists with Collectors.toMap

streams collectors maps
Intermediate 5 steps
php 
<?php
 
namespace App\Jobs;
 

Debouncing a Laravel shipping-rate job

queues debouncing atomic-locks
Advanced 9 steps
python 
from flask import Blueprint, render_template, redirect, url_for, session, request
from wtforms import Form, StringField, SelectField, IntegerField
from wtforms.validators import DataRequired, Email, NumberRange
 

A multi-step signup wizard in Flask

blueprints session-state form-validation
Intermediate 10 steps
javascript 
class ToastQueue {
  constructor(container, { duration = 4000, max = 3 } = {}) {
    this.container = container;
    this.duration = duration;

Building a rate-limited toast queue

queue dom manipulation throttling
Intermediate 8 steps
rust 
#[derive(Deserialize)]
pub struct CreateArticle {
    title: String,
    body: String,

Building a create endpoint in Axum

extractors json-deserialization sqlx
Intermediate 7 steps
java 
@Service
public class InventoryService {
 
    private final RestClient warehouseClient;

Bulkhead-protected HTTP calls in Spring

bulkhead resilience fallback
Intermediate 7 steps
go 
func UploadDocument(c *gin.Context) {
	fileHeader, err := c.FormFile("file")
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "file is required"})

Handling multipart uploads in Gin

multipart-upload validation error-handling
Intermediate 9 steps
php 
<?php
 
namespace App\Models\Concerns;
 

Building soft deletes as an Eloquent trait in Laravel

traits soft-delete global-scope
Intermediate 10 steps
rust 
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
 
use axum::body::Body;

A maintenance-mode gate in Axum

middleware shared-state atomics
Intermediate 7 steps
python 
from itertools import cycle
from collections import defaultdict
 
 

Round-robin task distribution in Python

round-robin iterators load-balancing
Intermediate 6 steps