Code Explainers

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php 
<?php
 
namespace App\Support;
 

Retry with exponential backoff in PHP

retry exponential-backoff error-handling
Intermediate 7 steps
typescript 
import { inject } from '@angular/core';
import { ResolveFn, Router, ActivatedRouteSnapshot } from '@angular/router';
import { catchError, of, EMPTY } from 'rxjs';
import { Article } from './models/article';

Prefetching route data with an Angular resolver

route-resolver dependency-injection rxjs
Intermediate 6 steps
python 
from itertools import islice
from typing import Iterable, Iterator, TypeVar
 
T = TypeVar("T")

Batching an iterable for bulk indexing

generators batching lazy-evaluation
Intermediate 7 steps
rust 
use axum::{
    extract::FromRef,
    http::StatusCode,
    response::{IntoResponse, Redirect},

Signed cookie sessions in Axum

sessions cookies authentication
Intermediate 8 steps
java 
package com.example.logs;
 
import java.io.IOException;
import java.io.UncheckedIOException;

Counting HTTP statuses with Java streams

streams regex file-io
Intermediate 6 steps
ruby 
class FundsTransfer
  class InsufficientFundsError < StandardError; end
 
  def initialize(source:, destination:, amount:)

Atomic money transfers with Rails transactions

service object database transactions row locking
Advanced 9 steps
php 
<?php
 
declare(strict_types=1);
 

Validating registration input with filter_var

validation sanitization filter_var
Intermediate 8 steps
typescript 
interface Order {
  id: number;
  customerId: string;
  total: number;

A type-safe groupBy in TypeScript

generics reduce type-inference
Intermediate 6 steps
python 
import time
from dataclasses import dataclass, field
 
from fastapi import Depends, FastAPI, HTTPException, Request, status

Token-bucket rate limiting in FastAPI

rate-limiting token-bucket dependency-injection
Advanced 10 steps
rust 
use axum::{
    http::StatusCode,
    response::{IntoResponse, Response},
    Json,

How a custom error type maps to HTTP in Axum

error-handling enums trait-implementation
Intermediate 7 steps
java 
@Service
public class GitHubClient {
 
    private final WebClient webClient;

Calling the GitHub API with Spring WebClient

reactive http-client dependency-injection
Intermediate 7 steps
javascript 
import { cookies } from 'next/headers';
import { NextResponse } from 'next/server';
import { SignJWT, jwtVerify } from 'jose';
 

JWT session cookies in a Next.js Route Handler

authentication jwt cookies
Intermediate 8 steps
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