Intermediate code explainers

ruby

class Money
  include Comparable
 
  CURRENCY_SYMBOLS = { usd: "$", eur: "€", gbp: "£" }.freeze

Building an immutable Money value object in Ruby

value-object immutability comparable

Intermediate 8 steps

php

function memoize(callable $fn): callable
{
    $cache = [];

How memoization works in PHP closures

memoization closures higher-order-functions

Intermediate 8 steps

typescript

import { Injectable, Logger } from '@nestjs/common';
import { Cron, CronExpression } from '@nestjs/schedule';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository, LessThan } from 'typeorm';

Scheduled session cleanup in NestJS

cron-scheduling background-jobs repository-pattern

Intermediate 7 steps

typescript

import {
  CallHandler,
  ExecutionContext,
  Injectable,

Wrapping responses in a NestJS interceptor

interceptors rxjs response-shaping

Intermediate 7 steps

rust

use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use std::thread;

Aggregating metrics across threads in Rust

concurrency shared-state mutex

Intermediate 7 steps

python

import argparse
import sys
from pathlib import Path

Building a subcommand CLI with argparse

cli argparse subcommands

Intermediate 6 steps

go

package main
 
import (
	"errors"

Parsing and validating CLI flags in Go

cli-parsing validation error-handling

Intermediate 8 steps

ruby

require "csv"
 
class SalesReport
  def initialize(path)

Aggregating CSV sales data in Ruby

data-aggregation memoization group_by

Intermediate 6 steps

javascript

'use server'
 
import { revalidatePath } from 'next/cache'
import { redirect } from 'next/navigation'

How a Next.js Server Action updates a post

server-actions authorization validation

Intermediate 7 steps

java

public class ThumbnailProcessor {
 
    private static final int MAX_CONCURRENCY = 4;

Bounded parallel thumbnail rendering in Java

concurrency thread-pool futures

Intermediate 7 steps

php

<?php
 
namespace App\Support;

Locale-aware formatting with PHP's intl extension

internationalization encapsulation constructor-injection

Intermediate 7 steps

typescript

type RetryOptions = {
  retries?: number;
  timeoutMs?: number;
  baseDelayMs?: number;

Retry with timeout and backoff in TypeScript

promises retry exponential-backoff

Intermediate 10 steps

python

from collections.abc import Mapping
from typing import Any, Iterator

Flattening nested config into dotted keys

recursion generators tree-traversal

Intermediate 7 steps

ruby

module DurationFormatter
  UNITS = [
    ['week', 604_800],
    ['day', 86_400],

Turning seconds into human-readable durations in Ruby

greedy-decomposition modular-arithmetic formatting

Intermediate 7 steps

javascript

const express = require('express');
 
const v1 = express.Router();

Versioning an API with Express Routers

api versioning routing modularity

Intermediate 10 steps

php

<?php
 
namespace App\Support;

Merging query params onto a URL in PHP

url-parsing query-strings immutability

Intermediate 8 steps

python

import csv
import io
from datetime import datetime

Streaming a CSV export in Flask

streaming generators csv

Intermediate 9 steps

go

package cache
 
import (
	"container/list"

Building a generic LRU cache in Go

lru-cache generics linked-list

Intermediate 8 steps