Code Explainers

Browse the library

java 
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = PasswordsMatchValidator.class)
public @interface PasswordsMatch {

Custom cross-field validation in Spring

bean-validation custom-constraints cross-field-validation
Intermediate 8 steps
go 
package logparse
 
import (
	"bufio"

Splitting multi-line logs with a Scanner

parsing streaming bufio
Intermediate 9 steps
typescript 
type TokenType = "keyword" | "string" | "comment" | "number" | "text";
 
interface Token {
  type: TokenType;

How a regex tokenizer highlights code

tokenizer regex lexing
Intermediate 10 steps
ruby 
module Rack
  class MaintenanceMode
    RETRY_AFTER = 3600
 

A Rack maintenance-mode middleware in Rails

middleware rack http-status
Intermediate 8 steps
php 
<?php
 
namespace App\Services;
 

How user impersonation works in Laravel

authentication authorization session
Intermediate 8 steps
javascript 
const express = require('express');
const router = express.Router();
 
router.get('/articles/:slug', async (req, res, next) => {

Conditional GET caching in Express

http-caching conditional-get routing
Intermediate 8 steps
rust 
use std::time::Duration;
 
#[derive(Debug, Clone, Copy)]
pub struct LatencyStats {

Computing latency percentiles in Rust

percentiles interpolation closures
Intermediate 6 steps
java 
public final class LogRedactor {
 
    private static final Pattern SECRET = Pattern.compile(
        "(?i)(password|token|api[_-]?key|secret|authorization)\\s*[=:]\\s*\\S+");

Streaming log redaction in Java

regex streaming-io try-with-resources
Intermediate 9 steps
go 
package handlers
 
import (
	"net/http"

Custom validators and binding in Gin

validation struct-tags error-handling
Intermediate 8 steps
python 
import secrets
 
from fastapi import Depends, FastAPI, HTTPException, Security, status
from fastapi.security import APIKeyHeader

API key authentication as a FastAPI dependency

authentication dependency-injection api-keys
Intermediate 8 steps
typescript 
import { Component, inject, signal } from '@angular/core';
import { CdkDragDrop, DragDropModule, moveItemInArray } from '@angular/cdk/drag-drop';
import { HttpClient } from '@angular/common/http';
import { finalize } from 'rxjs';

Drag-and-drop reordering with signals in Angular

drag-and-drop signals optimistic-update
Intermediate 8 steps
ruby 
class ImageNormalizer
  ORIENTATION_TRANSFORMS = {
    1 => ->(img) {},
    2 => ->(img) { img.flop },

Correcting EXIF orientation in Ruby

lookup-table lambdas image-processing
Intermediate 7 steps
php 
class OrderReceiptController extends Controller
{
    public function store(Request $request, Order $order)
    {

Handling receipt uploads in a Laravel controller

file-upload validation authorization
Intermediate 5 steps
javascript 
function parseHexColor(hex) {
  const cleaned = hex.trim().replace(/^#/, '');
 
  const expand = (short) =>

Parsing hex colors into RGBA channels

parsing bitwise regex
Intermediate 7 steps
ruby 
module RequestTagging
  class Middleware
    def initialize(app)
      @app = app

Per-request context with CurrentAttributes in Rails

middleware thread-safety logging
Intermediate 7 steps
go 
package hashring
 
import (
	"hash/crc32"

How consistent hashing works in Go

consistent-hashing load-balancing concurrency
Intermediate 8 steps
javascript 
import { useReducer, useCallback } from 'react';
 
function historyReducer(state, action) {
  const { past, present, future } = state;

Undo/redo form state with a React reducer

undo-redo reducer immutability
Intermediate 10 steps
python 
import hashlib
from collections import defaultdict
from pathlib import Path
 

Finding duplicate files by size then hash

hashing file-io deduplication
Intermediate 7 steps