Code Explainers

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typescript 
type CacheEntry<V> = {
  value: V;
  computedAt: number;
};

A TTL cache keyed by object identity

caching weakmap generics
Intermediate 8 steps
rust 
use std::fs::File;
use std::io::{self, BufRead, BufReader};
use std::path::Path;
 

Streaming lines from a gzip file in Rust

iterators io-streaming decompression
Intermediate 6 steps
ruby 
module MarkdownHelper
  ALLOWED_TAGS = %w[
    p br strong em del a ul ol li blockquote code pre
    h1 h2 h3 h4 h5 h6 hr img table thead tbody tr th td

Safely rendering Markdown in a Rails helper

sanitization markdown security
Intermediate 8 steps
php 
<?php
 
namespace App\Services;
 

Validating coupons before applying a discount in Laravel

validation guard clauses business rules
Intermediate 7 steps
python 
import functools
import time
 
from flask import current_app

Retrying deadlocked DB writes in Flask

decorators retry exponential-backoff
Intermediate 6 steps
go 
func HandleWebhook(store WebhookStore, dispatcher *EventDispatcher) gin.HandlerFunc {
	return func(c *gin.Context) {
		body, err := c.GetRawData()
		if err != nil {

Building a resilient webhook handler in Gin

webhooks dependency-injection signature-verification
Intermediate 9 steps
ruby 
class ActivityFeed
  include Enumerable
 
  Entry = Struct.new(:record, :type, :occurred_at, keyword_init: true) do

Building a paginated activity feed in Rails

enumerable pagination composition
Intermediate 9 steps
python 
import time
import logging
from threading import Lock
 

Rate-limiting noisy logs in Python

throttling thread-safety logging
Intermediate 6 steps
php 
<?php
 
namespace App\Services\Analytics;
 

Building a signup chart with Laravel's query builder

aggregation date-ranges query-builder
Intermediate 6 steps
rust 
use axum::{
    async_trait,
    extract::FromRequestParts,
    http::{request::Parts, StatusCode},

A proof-of-work extractor in Axum

proof-of-work extractors hashing
Advanced 9 steps
typescript 
import { Injectable, Scope } from '@nestjs/common';
import DataLoader from 'dataloader';
import { InjectRepository } from '@nestjs/typeorm';
import { In, Repository } from 'typeorm';

Batching queries with DataLoader in NestJS

dataloader batching n+1
Intermediate 7 steps
javascript 
const { z, ZodError } = require('zod');
 
function validate(schemas) {
  return (req, res, next) => {

A reusable Zod validation middleware for Express

middleware validation schema
Intermediate 8 steps
java 
public record TimeSlot(LocalDate day, LocalDateTime start, LocalDateTime end) {}
 
public class ScheduleAnalyzer {
 

Detecting calendar conflicts in Java

streams sorting sweep-line
Intermediate 8 steps
go 
func StreamLogs(c *gin.Context) {
	path := c.Query("file")
	if path == "" {
		c.JSON(http.StatusBadRequest, gin.H{"error": "missing file parameter"})

Streaming a live log tail with SSE in Gin

server-sent-events streaming channels
Advanced 10 steps
ruby 
class EditorHistory
  MAX_DEPTH = 100
 
  def initialize(initial = "")

How undo/redo history works in Ruby

undo-redo state-management immutability
Intermediate 9 steps
python 
import gzip
from fastapi import FastAPI, Request, Response
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.types import ASGIApp

Custom gzip middleware in FastAPI

middleware http-compression content-negotiation
Intermediate 9 steps
php 
<?php
 
function streamFileWithRanges(string $path, ?string $rangeHeader): void
{

How HTTP range requests stream files in PHP

http-range-requests streaming partial-content
Intermediate 10 steps
rust 
use std::collections::HashMap;
use std::sync::Arc;
 
use axum::body::Bytes;

A concurrent webhook dispatcher in Axum

trait-objects concurrency shared-state
Intermediate 9 steps