Code Explainers

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php 
<?php
 
namespace App\Http\Controllers;
 

Building a multi-step onboarding wizard in Laravel

session-state validation multi-step-forms
Intermediate 9 steps
typescript 
interface RunningStats {
  count: number;
  total: number;
  average: number;

Streaming running averages in TypeScript

generators streaming incremental-aggregation
Intermediate 6 steps
java 
package com.acme.catalog.persistence;
 
import jakarta.persistence.Column;
import jakarta.persistence.EntityListeners;

Auditing timestamps with a JPA MappedSuperclass in Spring

jpa auditing lifecycle-callbacks
Intermediate 5 steps
ruby 
require "thread"
 
class ConnectionPool
  class TimeoutError < StandardError; end

Building a thread-safe connection pool in Ruby

concurrency resource-pooling mutex
Advanced 8 steps
javascript 
import { createContext, useContext, useReducer, useCallback, useEffect } from 'react';
 
const AuthContext = createContext(null);
 

Building an auth context in React

context usereducer authentication
Intermediate 8 steps
python 
import json
import logging
import threading
from pathlib import Path

A hot-reloading config file watcher

file-watching thread-safety hot-reload
Intermediate 7 steps
go 
package dedup
 
import (
	"hash/fnv"

A rolling Bloom filter deduper in Go

bloom-filter deduplication concurrency
Advanced 7 steps
php 
<?php
 
namespace App\Http;
 

HTTP content negotiation in PHP

http content-negotiation parsing
Intermediate 9 steps
typescript 
import {
  IsEmail,
  IsNotEmpty,
  IsOptional,

How validation groups reuse one DTO in NestJS

validation dto decorators
Intermediate 9 steps
rust 
use axum::{
    extract::{FromRequestParts, Path, Query},
    http::{request::Parts, StatusCode},
    response::{IntoResponse, Redirect},

Signed download links as an Axum extractor

hmac custom-extractor authentication
Advanced 9 steps
java 
@Service
@RequiredArgsConstructor
public class ExchangeRateService {
 

Request-scoped rate caching in Spring

request-scope caching memoization
Advanced 6 steps
php 
<?php
 
namespace App\Listeners;
 

Generating responsive images in a Laravel listener

queued jobs event listeners image processing
Intermediate 7 steps
python 
class Parser:
    def __init__(self, text):
        self.tokens = self._tokenize(text)
        self.pos = 0

A recursive descent arithmetic parser

recursive-descent tokenizer operator-precedence
Intermediate 9 steps
javascript 
import { useDeferredValue, useMemo, useState } from "react";
 
function ProductSearch({ products }) {
  const [query, setQuery] = useState("");

Keeping search input snappy with useDeferredValue in React

concurrent-rendering deferred-value memoization
Intermediate 7 steps
rust 
use axum::{
    extract::{FromRef, FromRequestParts},
    http::{header, request::Parts, StatusCode},
    RequestPartsExt,

How a JWT extractor works in Axum

jwt authentication extractors
Intermediate 8 steps
typescript 
import { InjectionToken, inject, Provider, isDevMode } from '@angular/core';
import { WINDOW } from './window.token';
 
export interface AnalyticsConfig {

Layered config with an Angular InjectionToken

dependency-injection configuration factory-provider
Intermediate 8 steps
ruby 
class Admin::AccountsController < Admin::BaseController
  before_action :set_account, only: :destroy
 
  def destroy

A guarded destroy action in Rails

controllers callbacks transactions
Intermediate 8 steps
go 
package server
 
import (
	"net/http"

Rate limiting HTTP handlers with a token bucket

rate-limiting token-bucket middleware
Advanced 7 steps