Code Explainers

Intermediate code explainers

rust
use axum::{
    body::Body,
    extract::Path,
    http::{header, StatusCode},

Streaming file downloads in Axum

streaming file-serving path-traversal
Intermediate 8 steps
java
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;

Three ways to deduplicate a list by key in Java

streams deduplication collectors
Intermediate 6 steps
php
<?php
 
function verifyJwt(string $token, string $secret): array
{

Verifying an HS256 JWT in PHP

jwt hmac authentication
Intermediate 9 steps
python
from fastapi import FastAPI, Request, status
from fastapi.responses import JSONResponse
 
app = FastAPI()

Custom exception handlers in FastAPI

exception handling error responses separation of concerns
Intermediate 7 steps
ruby
class Article < ApplicationRecord
  before_validation :generate_slug, on: :create
 
  validates :slug, presence: true, uniqueness: true,

How URL slugs work in Rails

callbacks validations slugs
Intermediate 7 steps
ruby
class CheckoutService
  Result = Struct.new(:success?, :order, :error, keyword_init: true)
 
  def self.call(...)

How a Rails checkout service object works

service object transactions result object
Intermediate 9 steps
ruby
class User < ApplicationRecord
  has_one_attached :avatar
 
  validate :acceptable_avatar

Validating and serving avatars with Active Storage in Rails

active storage file uploads validation
Intermediate 9 steps
ruby
class Article < ApplicationRecord
  belongs_to :author
 
  default_scope { where(deleted_at: nil) }

How scopes compose in Rails

scopes query-composition activerecord
Intermediate 9 steps
ruby
class Employee < ApplicationRecord
  validates :name, presence: true
  validates :salary, numericality: { greater_than: 0 }
 

How STI models share behavior in Rails

single-table-inheritance inheritance method-overriding
Intermediate 8 steps
ruby
class ArticlesController < ApplicationController
  before_action :authenticate_user!
  before_action :set_article, only: %i[show edit update destroy]
  before_action :authorize_owner!, only: %i[edit update destroy]

How before_action filters guard a Rails controller

filters authorization callbacks
Intermediate 9 steps
ruby
class CreateCommentsWithCounterCache < ActiveRecord::Migration[7.1]
  def change
    create_table :posts do |t|
      t.string :title, null: false

How counter caches work in Rails

counter-cache migrations associations
Intermediate 6 steps
ruby
class ProductCatalog
  def featured_products
    Rails.cache.fetch("catalog/featured_products", expires_in: 12.hours) do
      Product.where(featured: true)

Caching patterns with Rails.cache.fetch

caching cache-keys expiry
Intermediate 5 steps
ruby
class RegistrationForm
  include ActiveModel::Model
  include ActiveModel::Attributes
 

How a Rails form object spans two models

form object validations transactions
Intermediate 7 steps
python
class FileManager:
    """A context manager that safely opens and closes a file."""
 
    def __init__(self, path, mode="r"):

Writing context managers in Python

context-managers resource-management exception-handling
Intermediate 6 steps
java
public class UnionFind {
    private final int[] parent;
    private final int[] rank;
    private int count;

How union-find with path compression works

disjoint-set path-compression union-by-rank
Intermediate 7 steps
go
package calc
 
import "testing"
 

Table-driven tests in Go

table-driven-tests error-handling subtests
Intermediate 7 steps
javascript
class Stack {
  #items = [];
 
  push(value) {

Building a Stack with private fields

data-structures encapsulation iterators
Intermediate 7 steps
typescript
import {
  Injectable,
  NestInterceptor,
  ExecutionContext,

How a NestJS logging interceptor works

interceptors rxjs logging
Intermediate 5 steps