Code Explainers

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php 
<?php
 
namespace App\Services;
 

Building signed, expiring download URLs in PHP in Laravel

hmac url-signing authentication
Intermediate 7 steps
rust 
use std::path::PathBuf;
 
use clap::{Parser, Subcommand, ValueEnum};
 

Building a CLI with clap's derive macros

cli derive-macros argument-parsing
Intermediate 10 steps
java 
@RestController
@RequestMapping("/api/files")
public class FileUploadController {
 

Handling secure file uploads in Spring

file-upload input-validation path-traversal
Intermediate 10 steps
ruby 
def collatz_lengths
  Enumerator.new do |y|
    n = 1
    loop do

Building infinite sequences with lazy enumerators

lazy-evaluation enumerators infinite-sequences
Intermediate 8 steps
go 
package middleware
 
import (
	"context"

Correlation ID tracing middleware in Gin

middleware request tracing structured logging
Intermediate 7 steps
typescript 
import { Component, computed, inject, signal } from '@angular/core';
import { FormBuilder, ReactiveFormsModule, Validators } from '@angular/forms';
import { CommonModule } from '@angular/common';
 

Building a signup stepper in Angular

signals reactive-forms form-validation
Intermediate 10 steps
python 
from dataclasses import dataclass
from typing import Optional
 
from sqlalchemy import select, func

Building a pagination helper with SQLAlchemy

pagination dataclass computed-properties
Intermediate 8 steps
javascript 
class DOMBatcher {
  constructor() {
    this.reads = [];
    this.writes = [];

Batching DOM reads and writes to avoid layout thrash

batching requestanimationframe layout-thrashing
Intermediate 8 steps
php 
<?php
 
declare(strict_types=1);
 

A single-action JSON user controller in PHP

invokable-class json-api validation
Intermediate 7 steps
rust 
use std::sync::Arc;
use axum::{
    body::Body,
    extract::{Extension, State},

Passing per-request context through Axum middleware

middleware request-context dependency-injection
Intermediate 8 steps
java 
package com.example.fs;
 
import java.io.IOException;
import java.nio.file.FileSystems;

Watching a directory with Java NIO

file-io event-loop resource-management
Intermediate 8 steps
go 
package web
 
import (
	"embed"

Serving embedded static assets in Go

embed static-assets http-handler
Intermediate 8 steps
typescript 
type Change =
  | { kind: "added"; path: string; value: unknown }
  | { kind: "removed"; path: string; value: unknown }
  | { kind: "updated"; path: string; from: unknown; to: unknown };

Building a recursive deep-diff in TypeScript

recursion discriminated-unions type-guards
Intermediate 9 steps
python 
from datetime import timedelta
 
from django.contrib.sessions.models import Session
from django.core.management.base import BaseCommand

A batched session-cleanup command in Django

management-command batch-processing database-cleanup
Intermediate 7 steps
javascript 
function createCountdownTimer(durationSeconds, { onTick, onComplete } = {}) {
  let remaining = durationSeconds;
  let intervalId = null;
 

Building a countdown timer with closures

closures factory-function timers
Intermediate 9 steps
php 
<?php
 
namespace App\Services\Provisioning;
 

Sequencing site setup with Laravel job chains

job chains queues async workflows
Intermediate 6 steps
rust 
use std::collections::HashMap;
use std::fmt;
 
#[derive(Debug)]

Parsing a config file with typed errors in Rust

error-handling enums parsing
Intermediate 9 steps
java 
public final class QueryParams {
 
    private final Map<String, List<String>> params;
 

Parsing and building URL query strings in Java

parsing multimap url-encoding
Intermediate 9 steps