Code Explainers

Browse the library

ruby 
require 'json'
require 'set'
 
class SensitiveScrubber

Recursively scrubbing secrets from JSON

recursion data-masking pattern-matching
Intermediate 7 steps
python 
from django.conf import settings
from django.contrib.auth import get_user_model
from django.core.mail import EmailMultiAlternatives
from django.db.models.signals import post_save

Sending a welcome email with Django signals

signals email user-activation
Intermediate 8 steps
rust 
use std::collections::HashMap;
 
pub struct Memoizer<K, V, F> {
    cache: HashMap<K, V>,

A generic memoizer in Rust

memoization generics caching
Intermediate 6 steps
javascript 
const transitions = {
  cart: { checkout: 'shipping' },
  shipping: { submitAddress: 'payment', back: 'cart' },
  payment: { submitPayment: 'review', back: 'shipping' },

A finite state machine for checkout flow

state-machine event-driven data-driven-design
Intermediate 7 steps
java 
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = StrongPasswordValidator.class)
@Documented

Building a custom @StrongPassword validator in Spring

bean-validation annotations regex
Intermediate 7 steps
typescript 
import { Component } from '@angular/core';
import { FormControl, ReactiveFormsModule } from '@angular/forms';
import { HttpClient } from '@angular/common/http';
import { AsyncPipe } from '@angular/common';

Reactive type-ahead search in Angular

rxjs reactive-forms debounce
Intermediate 9 steps
php 
<?php
 
namespace App\Observers;
 

How Eloquent observers hook lifecycle events in Laravel

observers lifecycle-hooks queues
Intermediate 6 steps
ruby 
class ReportBatcher
  BATCH_SIZE = 500
 
  def initialize(account)

Batching monthly email summaries in Rails

batching service-object background-jobs
Intermediate 7 steps
python 
import csv
import io
from datetime import date
 

Streaming a CSV export in FastAPI

streaming async-generators csv
Advanced 8 steps
rust 
use std::collections::HashMap;
 
#[derive(Debug, Clone)]
struct Order {

Aggregating Rust data with fold and entry

fold hashmap ownership
Intermediate 6 steps
go 
func (h *TransactionHandler) ExportCSV(c *gin.Context) {
	ctx := c.Request.Context()
	filters := parseTransactionFilters(c)
 

Streaming a CSV export in Gin

streaming csv-export database-cursor
Intermediate 8 steps
php 
<?php
 
namespace App\Rules;
 

How a custom phone validation rule works in Laravel

validation custom-rules dependency
Intermediate 6 steps
ruby 
class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true, counter_cache: true
  belongs_to :author, class_name: "User"
 

How polymorphic comments work in Rails

polymorphic-association concerns counter-cache
Intermediate 8 steps
python 
import json
import logging
 
import stripe

Handling Stripe webhooks in Django

webhooks signature-verification idempotency
Intermediate 7 steps
javascript 
import { useState, useEffect, useCallback, useRef } from "react";
 
export function usePersistentForm(storageKey, initialValues) {
  const [values, setValues] = useState(() => {

A React hook that persists form state to localStorage

custom-hooks localstorage debounce
Intermediate 9 steps
rust 
use axum::{extract::State, http::StatusCode, response::IntoResponse, Json};
use serde::{Deserialize, Serialize};
use uuid::Uuid;
 

Building a typed create_user handler in Axum

serde extractors sqlx
Intermediate 7 steps
java 
@Component
public class JwtAuthenticationFilter extends OncePerRequestFilter {
 
    private final JwtTokenProvider tokenProvider;

How a JWT auth filter works in Spring

authentication jwt servlet-filter
Intermediate 8 steps
typescript 
function throttle<T extends (...args: any[]) => void>(
  fn: T,
  limit: number
): (...args: Parameters<T>) => void {

Building a trailing-edge throttle in TypeScript

throttling closures generics
Intermediate 7 steps