Code Explainers

Browse the library

python 
import time
from concurrent.futures import ThreadPoolExecutor, as_completed
from pathlib import Path
 

Parallel file downloads with a thread pool

concurrency thread-pool streaming-io
Intermediate 8 steps
rust 
use std::collections::HashMap;
 
#[derive(Debug, Clone)]
struct Record {

Batched aggregation with fold in Rust

iterators fold hashmap
Intermediate 9 steps
typescript 
import { Directive, ElementRef, HostListener, Input, OnDestroy, OnInit } from '@angular/core';
 
@Directive({
  selector: '[appTrapFocus]',

Building a focus-trap directive in Angular

accessibility focus-management dom
Intermediate 9 steps
java 
package com.example.payments.config;
 
import com.stripe.StripeClient;
import org.springframework.beans.factory.annotation.Value;

Swapping payment gateways by profile in Spring

dependency-injection profiles configuration
Intermediate 6 steps
javascript 
const crypto = require('crypto');
 
function securityHeaders(options = {}) {
  const {

A configurable security-headers middleware in Express

middleware http-headers content-security-policy
Intermediate 7 steps
go 
package validate
 
import (
	"fmt"

Struct validation with reflection in Go

reflection struct-tags validation
Intermediate 7 steps
php 
use Illuminate\Support\Facades\Route;
use App\Http\Controllers\Admin\DashboardController;
use App\Http\Controllers\Admin\UserController;
use App\Http\Controllers\Admin\ReportController;

How nested route groups compose in Laravel

routing middleware authorization
Intermediate 8 steps
ruby 
class ParamCoercer
  TYPES = {
    integer: ->(v) { Integer(v) },
    float:   ->(v) { Float(v) },

Coercing request params by schema in Ruby

lambdas type-coercion lookup-table
Intermediate 7 steps
python 
from datetime import datetime
from zoneinfo import ZoneInfo
 
 

Timezone-safe datetime handling in Python

timezones datetime normalization
Intermediate 4 steps
rust 
use std::env;
use std::time::Duration;
 
#[derive(Debug, Clone)]

Loading typed config from environment variables in Rust

configuration error-handling generics
Intermediate 7 steps
typescript 
type AsyncFn<A extends unknown[], R> = (...args: A) => Promise<R>;
 
interface MemoizeOptions<A extends unknown[]> {
  keyFn?: (...args: A) => string;

Memoizing async functions with TTL in TypeScript

memoization generics promises
Advanced 8 steps
java 
public class EventBus {
 
    private final Map<Class<?>, List<Subscriber>> subscribers = new ConcurrentHashMap<>();
    private final Executor executor;

Building an annotation-driven EventBus in Java

publish-subscribe reflection annotations
Intermediate 7 steps
javascript 
import { useRef, useCallback, useEffect, useState } from "react";
 
function useThrottle(callback, delay) {
  const lastRun = useRef(0);

Building a throttle hook in React

throttling custom-hooks refs
Intermediate 8 steps
go 
package middleware
 
import (
	"bytes"

Verifying webhook HMAC signatures in Gin

hmac middleware webhooks
Intermediate 7 steps
php 
final class TokenBucketLimiter
{
    private float $tokens;
    private float $lastRefill;

How a token bucket rate limiter works

rate-limiting token-bucket throttling
Intermediate 7 steps
ruby 
module Api
  module V2
    class ArticlesController < Api::BaseController
      before_action :set_article, only: %i[show update destroy]

Building a versioned JSON API controller in Rails

rest-api serialization pagination
Intermediate 10 steps
python 
import shutil
import uuid
from pathlib import Path
 

Safe avatar uploads in FastAPI

file-upload validation streaming
Intermediate 8 steps
typescript 
import { Injectable, Scope, Inject } from '@nestjs/common';
import { REQUEST } from '@nestjs/core';
import { Request } from 'express';
 

Request-scoped context service in NestJS

dependency-injection request-scope immutability
Intermediate 8 steps