Code Explainers · highlit

python

from datetime import timedelta
 
from flask import Blueprint, current_app, make_response, redirect, request, url_for
from itsdangerous import URLSafeTimedSerializer, BadSignature, SignatureExpired

How signed remember-me cookies work in Flask

authentication signed-cookies session-management

Intermediate 8 steps

java

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.module.SimpleModule;

Serializing Money to JSON in Spring

serialization jackson money

Intermediate 8 steps

rust

use std::{collections::HashSet, sync::Arc};
 
use axum::{
    body::Body,

Feature-flag middleware in Axum

middleware async shared-state

Advanced 7 steps

php

<?php
 
namespace App\Services;

Building a valid iCalendar feed in PHP in Laravel

ical serialization formatting

Intermediate 8 steps

ruby

class ApplicationController < ActionController::Base
  ALLOWED_REDIRECT_HOSTS = [nil, ENV.fetch("APP_HOST", "app.example.com")].freeze
 
  def store_return_to(location = request.fullpath)

Safe post-login redirects in Rails

open-redirect session authentication

Intermediate 9 steps

php

<?php
 
namespace App\View\Components;

Building a breadcrumb component in Laravel

blade components url parsing string manipulation

Intermediate 8 steps

javascript

import { unstable_cache, revalidateTag } from 'next/cache'
import { db } from '@/lib/db'
 
export const getDashboardStats = unstable_cache(

Caching dashboard stats in Next.js

caching cache-invalidation tag-based-revalidation

Intermediate 8 steps

java

@Component
@Order(Ordered.HIGHEST_PRECEDENCE)
public class TenantResolutionFilter extends OncePerRequestFilter {

How a tenant-resolution filter works in Spring

multi-tenancy servlet-filter thread-local

Intermediate 8 steps

rust

pub fn format_size(bytes: u64) -> String {
    const UNITS: [&str; 7] = ["B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"];
 
    if bytes < 1024 {

Formatting byte counts as human-readable sizes

bit-manipulation formatting unit-conversion

Intermediate 5 steps

python

import click
from flask.cli import AppGroup
 
from . import db

Custom user CLI commands in Flask

cli click command-group

Intermediate 7 steps

typescript

interface ParsedName {
  first: string;
  middle: string;
  last: string;

Parsing human names into structured parts

parsing string-manipulation normalization

Intermediate 9 steps

go

package middleware
 
import (
	"compress/gzip"

How gzip HTTP middleware works in Go

middleware compression object-pooling

Intermediate 7 steps

ruby

require 'set'
 
class DirectoryWatcher
  def initialize(path, pattern: '**/*', interval: 1.0)

Polling for file changes in Ruby

polling filesystem diffing

Intermediate 7 steps

php

<?php
 
namespace App\Experiments;

Weighted random selection in PHP

weighted-random cumulative-sum sampling

Intermediate 8 steps

javascript

import { Component } from 'react';
import { reportError } from './services/telemetry';
 
export class ErrorBoundary extends Component {

How a React ErrorBoundary works

error-handling lifecycle-methods render-props

Intermediate 8 steps

java

@Repository
public interface SubscriptionRepository extends JpaRepository<Subscription, Long> {
 
    @Modifying(clearAutomatically = true, flushAutomatically = true)

Bulk JPQL updates in a Spring Data repository

jpql bulk-update modifying-query

Intermediate 5 steps

rust

use base64::engine::general_purpose::{STANDARD, URL_SAFE_NO_PAD};
use base64::{DecodeError, Engine};
 
pub fn encode_standard(data: &[u8]) -> String {

Base64 encode and decode in Rust

base64 encoding error-handling

Beginner 7 steps

python

import heapq
from datetime import datetime
from pathlib import Path
from typing import Iterator, NamedTuple

Merging sorted log files with heapq

generators heapq lazy-evaluation

Intermediate 6 steps