Code Explainers
Intermediate code explainers
java
public record ServerConfig( String host, int port, Duration timeout,
Loading typed config into a Java record
records
factory-methods
parsing
Intermediate
7 steps
java
public final class IbanValidator { private static final Map<String, Integer> COUNTRY_LENGTHS = Map.ofEntries( Map.entry("DE", 22), Map.entry("FR", 27), Map.entry("GB", 22),
Validating IBANs with the mod-97 checksum
validation
checksum
modular-arithmetic
Intermediate
8 steps
ruby
class LRUCache def initialize(capacity) raise ArgumentError, "capacity must be positive" unless capacity.positive?
How an LRU cache works in Ruby
caching
eviction
hash-ordering
Intermediate
7 steps
python
import re from collections import Counter from pathlib import Path
Ranking the top words in a PDF
text-processing
regex
counting
Intermediate
6 steps
go
package tsvio import ( "bufio"
Reading and writing TSV records in Go
parsing
io-streams
error-handling
Intermediate
10 steps
rust
pub struct Fibonacci { current: u64, next: u64, }
A Fibonacci iterator in Rust
iterators
traits
lazy-evaluation
Intermediate
6 steps
php
<?php namespace App\Http\Middleware;
Verifying GitHub webhook signatures in Laravel
middleware
hmac
webhooks
Intermediate
5 steps
java
@Configuration @EnableWebSecurity public class OAuth2SecurityConfig {
How OIDC login works in Spring Security
oauth2
openid-connect
authorization
Intermediate
8 steps
ruby
class QueryParser def self.parse(query_string) new(query_string).parse end
Parsing nested query strings in Ruby
parsing
recursion
tokenization
Intermediate
9 steps
python
import django_filters from django import forms from django.utils import timezone
Building a date-range FilterSet in Django
filtering
querysets
form-widgets
Intermediate
6 steps
typescript
type CountdownState = { deadline: number; onTick: (remaining: number) => void; onComplete: () => void;
A countdown timer that survives reloads
persistence
timers
localstorage
Intermediate
10 steps
go
package config import ( "fmt"
Loading and saving YAML config in Go
yaml
struct-tags
defaults
Intermediate
8 steps
php
<?php namespace App\Models;
How Eloquent scopes model order status in Laravel
query scopes
state machine
eloquent
Intermediate
7 steps
java
@RestController @RequestMapping("/api/reports") public class OrderReportController {
Streaming a CSV export in Spring
streaming
csv-export
backpressure
Intermediate
9 steps
ruby
class Article < ApplicationRecord belongs_to :author, class_name: "User" has_many :taggings, dependent: :destroy has_many :tags, through: :taggings
How scopes compose in Rails
scopes
activerecord
query-composition
Intermediate
8 steps
typescript
type QueuedRequest = { id: string; url: string; method: string;
A retry queue with exponential backoff
retry
exponential-backoff
persistence
Intermediate
10 steps
ruby
class Order class InvalidTransition < StandardError; end TRANSITIONS = {
A state machine for order transitions in Ruby
state-machine
data-driven
error-handling
Intermediate
8 steps
python
from flask import Blueprint, jsonify, request, abort v1 = Blueprint("users_v1", __name__) v2 = Blueprint("users_v2", __name__)
Versioning a Flask API with Blueprints
api versioning
blueprints
rest
Intermediate
7 steps