Code Explainers

Browse the library

java 
public class DuplicateFinder {
 
    public Map<String, List<Path>> findDuplicates(Path root) throws IOException {
        Map<String, List<Path>> byHash = new HashMap<>();

Finding duplicate files by content hash

hashing file-io streams
Intermediate 8 steps
php 
<?php
 
namespace App\Support;
 

Normalizing phone numbers to E.164 in PHP

input-validation normalization regular-expressions
Intermediate 8 steps
ruby 
class QueryProxy
  ALLOWED = %i[where limit offset order includes distinct].freeze
 
  def initialize(relation, operations = [])

Building a lazy query proxy in Ruby

metaprogramming method_missing lazy-evaluation
Advanced 7 steps
javascript 
class InfiniteScroll {
  constructor(sentinel, { loadMore, root = null, rootMargin = '200px' } = {}) {
    this.sentinel = sentinel;
    this.loadMore = loadMore;

Infinite scroll with IntersectionObserver

intersectionobserver pagination async
Intermediate 10 steps
java 
@Component
public class OrderRecoveryHandler {
 
    private final RabbitTemplate rabbitTemplate;

Dead-letter recovery with Spring AMQP

dead-letter-queue retry exponential-backoff
Advanced 9 steps
ruby 
class Debouncer
  def initialize(delay:)
    @delay = delay
    @mutex = Mutex.new

A thread-safe debouncer in Ruby

concurrency debouncing mutex
Advanced 5 steps
go 
package storage
 
import (
	"context"

A SQLite-backed order store in Go

database/sql sqlite error-wrapping
Intermediate 7 steps
php 
final class Route
{
    private string $regex;
    private array $paramNames = [];

Compiling route patterns into regex in PHP

routing regex parsing
Intermediate 8 steps
javascript 
import { forwardRef, useImperativeHandle, useRef, useState } from 'react';
 
const TextField = forwardRef(function TextField(
  { label, error, onChange, ...props },

Exposing an imperative handle in React

forwardref useimperativehandle refs
Advanced 8 steps
typescript 
import {
  CanActivate,
  ExecutionContext,
  Injectable,

How guards chain auth in NestJS

guards authentication authorization
Intermediate 8 steps
python 
from fastapi import APIRouter, Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from sqlalchemy.orm import Session

Chaining auth dependencies in FastAPI

dependency-injection jwt-authentication authorization
Intermediate 8 steps
java 
@Component
public class CorrelationIdWebFilter implements WebFilter, Ordered {
 
    public static final String CORRELATION_ID_HEADER = "X-Correlation-Id";

Correlation IDs in a Spring WebFlux filter

reactive web filter correlation id
Advanced 7 steps
ruby 
require "net/http"
require "json"
 
class UrlFetcher

A thread-pool URL fetcher in Ruby

concurrency thread-pool queues
Intermediate 8 steps
rust 
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
use std::thread;
 

A round-robin worker pool in Rust

concurrency thread-pool channels
Intermediate 7 steps
go 
package auth
 
import (
	"errors"

Hashing and verifying passwords with bcrypt in Go

password-hashing bcrypt error-handling
Intermediate 7 steps
php 
public function customerTotals(Request $request): Collection
{
    return DB::table('orders')
        ->join('customers', 'customers.id', '=', 'orders.customer_id')

Building an aggregate report with Laravel's query builder

query builder aggregation conditional queries
Intermediate 8 steps
typescript 
import { useState, useCallback } from 'react';
 
type Todo = {
  id: string;

Optimistic UI updates in a React hook

optimistic-updates custom-hooks error-handling
Intermediate 8 steps
python 
from flask import Blueprint, request, url_for, jsonify, abort
from flask.views import MethodView
 
from .models import Article, db

Building a paginated JSON API with Flask MethodView

rest-api pagination class-based-views
Intermediate 10 steps