Intermediate code explainers

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

ruby

# Curry a multi-argument lambda so it can be applied one argument at a time.
add = ->(a, b, c) { a + b + c }
 
# Proc#curry returns a curried version that collects arguments incrementally.

Currying lambdas and methods in Ruby

currying closures partial-application

Intermediate 7 steps

php

<?php
 
class Entity
{

PHP magic methods for dynamic attributes

magic-methods overloading encapsulation

Intermediate 6 steps

rust

/// A custom iterator that yields Fibonacci numbers up to a maximum value.
pub struct Fibonacci {
    current: u64,
    next: u64,

Building a custom Fibonacci iterator in Rust

iterators traits state-machine

Intermediate 6 steps