Code Explainers

Browse the library

ruby 
require "charlock_holmes"
 
class TextFileNormalizer
  DEFAULT_CONFIDENCE = 60

Normalizing text files to clean UTF-8 in Ruby

encoding text-processing file-io
Intermediate 8 steps
rust 
use rand::distributions::{Alphanumeric, DistString};
use rand::rngs::OsRng;
 
#[derive(Debug, Clone, PartialEq, Eq)]

A newtype wrapper for API tokens in Rust

newtype-pattern randomness encapsulation
Intermediate 6 steps
python 
from datetime import datetime, timezone
 
_INTERVALS = (
    ("year", 60 * 60 * 24 * 365),

Building a human-friendly time_ago helper

datetime timezones formatting
Intermediate 5 steps
php 
<?php
 
namespace App\Validation;
 

Building a reusable address form validator in PHP

validation error-accumulation regex
Intermediate 9 steps
typescript 
export function isValidCardNumber(input: string): boolean {
  const digits = input.replace(/[\s-]/g, "");
 
  if (!/^\d{12,19}$/.test(digits)) {

Validating card numbers with the Luhn check

luhn-algorithm checksum input-validation
Intermediate 7 steps
javascript 
const { Pool } = require('pg');
 
const pool = new Pool({
  connectionString: process.env.DATABASE_URL,

Per-request Postgres connections in Express

connection-pooling middleware transactions
Intermediate 8 steps
go 
package logging
 
import (
	"fmt"

Redacting secrets with Go reflection

reflection recursion struct-tags
Advanced 10 steps
java 
public class RequestThrottler {
 
    private final Semaphore permits;
    private final long acquireTimeoutMillis;

Bounding concurrency with a Semaphore in Java

concurrency semaphore rate-limiting
Intermediate 6 steps
ruby 
require 'date'
require 'set'
 
class BusinessDayCalculator

Counting business days in Ruby

dates sets ranges
Intermediate 8 steps
rust 
pub fn normalize_path(input: &str) -> String {
    let is_absolute = input.starts_with('/');
    let has_trailing_slash = input.len() > 1 && input.ends_with('/');
    let mut stack: Vec<&str> = Vec::new();

Normalizing filesystem paths in Rust

string-processing stack path-manipulation
Intermediate 8 steps
python 
import time
import threading
from flask import Flask, request, jsonify, g
 

A token-bucket rate limiter in Flask

rate-limiting token-bucket middleware
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Controllers;
 

A cached autocomplete endpoint in Laravel

caching validation query-ranking
Intermediate 8 steps
typescript 
interface UserAgentInfo {
  browser: { name: string; version: string };
  os: { name: string; version: string };
  device: 'mobile' | 'tablet' | 'desktop';

Parsing a user-agent string with ordered rules

regex parsing pattern-matching
Intermediate 9 steps
javascript 
const express = require('express');
const router = express.Router();
const db = require('../db');
 

Building a paginated orders page in Express

pagination routing sql-queries
Intermediate 7 steps
go 
package middleware
 
import (
	"context"

Per-tenant daily rate limiting in Gin

rate-limiting middleware redis
Intermediate 8 steps
java 
public List<DailySample> backfillMissingDates(List<DailySample> samples, double fillValue) {
    if (samples.isEmpty()) {
        return List.of();
    }

Backfilling gaps in a daily time series in Java

streams time-series treemap
Intermediate 5 steps
ruby 
class Document < ApplicationRecord
  class StaleObjectError < StandardError
    def initialize(id)
      super("Document ##{id} was modified by another process")

Optimistic locking with retries in Rails

optimistic-locking concurrency transactions
Advanced 8 steps
rust 
use axum::{
    extract::Query,
    response::IntoResponse,
    Json,

Parsing query strings in Axum handlers

deserialization query-parameters defaults
Intermediate 7 steps