Code Explainers

Browse the library

rust
use std::sync::{mpsc, Arc, Mutex};
use std::thread;
use std::time::Duration;
 

Building a thread pool in Rust

concurrency channels thread-pool
Advanced 9 steps
python
from collections.abc import Mapping
from typing import Any, Iterator
 
 

Flattening nested config into dotted keys

recursion generators tree-traversal
Intermediate 7 steps
ruby
module DurationFormatter
  UNITS = [
    ['week', 604_800],
    ['day', 86_400],

Turning seconds into human-readable durations in Ruby

greedy-decomposition modular-arithmetic formatting
Intermediate 7 steps
javascript
const express = require('express');
 
const v1 = express.Router();
 

Versioning an API with Express Routers

api versioning routing modularity
Intermediate 10 steps
java
public class SortedListMerger {
 
    public static int[] merge(int[] a, int[] b) {
        int[] result = new int[a.length + b.length];

Merging two sorted arrays in Java

two-pointers merging arrays
Beginner 6 steps
php
<?php
 
namespace App\Support;
 

Merging query params onto a URL in PHP

url-parsing query-strings immutability
Intermediate 8 steps
typescript
import { Pipe, PipeTransform, ChangeDetectorRef, NgZone, OnDestroy } from '@angular/core';
 
@Pipe({
  name: 'timeAgo',

A self-refreshing timeAgo pipe in Angular

impure-pipe change-detection timers
Advanced 10 steps
python
import csv
import io
from datetime import datetime
 

Streaming a CSV export in Flask

streaming generators csv
Intermediate 9 steps
go
package cache
 
import (
	"container/list"

Building a generic LRU cache in Go

lru-cache generics linked-list
Intermediate 8 steps
php
<?php
 
class ImageUploadService
{

Validating file uploads safely in PHP

file-upload input-validation security
Intermediate 8 steps
ruby
class Comment < ApplicationRecord
  belongs_to :post
  belongs_to :author, class_name: "User"
 

Live-updating comments with Turbo in Rails

turbo-streams callbacks associations
Intermediate 8 steps
python
import time
from collections import defaultdict
from threading import Lock
 

Sliding-window login rate limiting in Flask

rate-limiting sliding-window thread-safety
Intermediate 7 steps
rust
use std::time::Instant;
use tracing::info;
 
pub struct Timer {

A scope-guard timer with Drop in Rust

raii drop-guard timing
Intermediate 7 steps
javascript
const RATE_LIMIT = 100;
const WINDOW_MS = 60 * 1000;
const BLOCK_MS = 5 * 60 * 1000;
 

Building a rate-limiting middleware in Express

rate-limiting middleware closures
Intermediate 9 steps
go
package model
 
import (
	"encoding/json"

Custom JSON marshaling in Go

json serialization interfaces
Intermediate 5 steps
java
import java.util.ArrayDeque;
import java.util.Deque;
 
public final class RollingAverage {

A rolling average over a sliding window

sliding-window running-sum deque
Intermediate 7 steps
typescript
const DIVISIONS: { amount: number; unit: Intl.RelativeTimeFormatUnit }[] = [
  { amount: 60, unit: "seconds" },
  { amount: 60, unit: "minutes" },
  { amount: 24, unit: "hours" },

Human-readable relative times with Intl

internationalization date-formatting lookup-table
Intermediate 7 steps
php
<?php
 
namespace App\View;
 

Building a safe HTML escaper in PHP

security xss escaping
Intermediate 6 steps