Code Explainers · highlit

rust

use std::net::SocketAddr;
use std::time::Duration;
 
use axum::{routing::get, Json, Router};

Per-IP rate limiting in Axum with tower-governor

rate-limiting middleware tower

Intermediate 7 steps

php

<?php
 
namespace App\Providers;

Binding a payment gateway in Laravel

dependency-injection service-container interface-binding

Intermediate 7 steps

ruby

class ProductsController < ApplicationController
  def index
    @products = Product
      .includes(:category, :brand)

Building a safe filterable product index in Rails

query objects scopes strong parameters

Intermediate 8 steps

java

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.math.BigInteger;

A thread-safe memoized factorial cache

memoization thread-safety caching

Intermediate 6 steps

typescript

export function chunk<T>(items: readonly T[], size: number): T[][] {
  if (size <= 0 || !Number.isInteger(size)) {
    throw new RangeError(`chunk size must be a positive integer, got ${size}`);
  }

Splitting work into sequential batches in TypeScript

generics async-await batching

Intermediate 5 steps

go

package handlers
 
import (
	"net/http"

Cookie-based sessions in Gin

authentication cookies middleware

Intermediate 7 steps

python

from pathlib import Path
 
 
def print_tree(root, prefix="", show_hidden=False):

Printing a directory tree with recursion

recursion filesystem sorting

Intermediate 6 steps

php

<?php
 
namespace App\Http\Controllers\Auth;

How a Laravel registration endpoint works

validation database-transactions events

Intermediate 8 steps

ruby

module LogParser
  class AccessLogStreamer
    SEVERITY_PATTERN = /\b(ERROR|WARN|FATAL)\b/

Streaming log lines with a Ruby enumerator

enumerators lazy-iteration regex-matching

Intermediate 6 steps

java

@RestController
@RequestMapping("/webhooks/stripe")
public class StripeWebhookController {

How a Stripe webhook controller works in Spring

webhooks signature-verification event-handling

Intermediate 7 steps

typescript

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable, throwError, timer } from 'rxjs';
import { mergeMap, retryWhen } from 'rxjs/operators';

Exponential backoff retries in Angular

retry exponential-backoff rxjs

Advanced 7 steps

javascript

import Papa from 'papaparse';
 
const MAX_SIZE = 5 * 1024 * 1024;

Validating and parsing CSV uploads in the browser

promises csv-parsing validation

Intermediate 8 steps

go

package validators
 
import (
	"regexp"

Custom validators in Gin

validation sync.once regexp

Intermediate 5 steps

python

from dataclasses import dataclass, fields, MISSING
from typing import get_type_hints, get_origin, get_args, Union

Type-checking dataclasses at runtime

dataclasses type-hints runtime-validation

Advanced 8 steps

rust

use axum::{
    body::Body,
    extract::Request,
    http::{header::HeaderValue, HeaderName},

Request ID middleware in Axum

middleware tracing request-extensions

Intermediate 7 steps

php

<?php
 
namespace App\Http\Controllers;

Handling avatar uploads in Laravel

file-upload image-processing validation

Intermediate 8 steps

ruby

class HostnameValidator < ActiveModel::EachValidator
  MAX_LENGTH = 253
  LABEL = /\A(?!-)[a-z0-9-]{1,63}(?<!-)\z/i

Writing a custom hostname validator in Rails

validation custom validator regex

Intermediate 8 steps

ruby

class PaymentsController < ApplicationController
  before_action :require_idempotency_key
 
  def create

Idempotent payment creation in Rails

idempotency transactions race-conditions

Advanced 10 steps