Code Explainers

Code explainers tagged #recursion

php 
final class ConfigResolver
{
    private array $merged;
 

Layered config merging in PHP

recursion immutability variadics
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
rust 
use std::fs;
use std::io;
use std::path::{Path, PathBuf};
 

Recursive file search by extension in Rust

recursion filesystem error-handling
Intermediate 8 steps
ruby 
module ConfigMerge
  module_function
 
  def deep_merge(base, override)

Recursively merging nested config hashes in Ruby

recursion hash-merge immutability
Intermediate 8 steps
ruby 
module DeepFreeze
  module_function
 
  def call(obj)

Recursively freezing nested Ruby data

recursion immutability pattern matching
Intermediate 9 steps
python 
from functools import lru_cache
import math
 
 

Memoizing number theory with lru_cache

memoization number-theory caching
Intermediate 8 steps
python 
from collections import ChainMap
from functools import reduce
from typing import Any, Iterable, Mapping
 

Five ways to merge dicts in Python

dictionaries merging recursion
Intermediate 8 steps
ruby 
class ConfigFlattener
  def initialize(config)
    @config = config
  end

Flattening nested config into dotted keys

recursion hashes tree-traversal
Intermediate 8 steps
ruby 
def build_tree(rows, root_id: nil)
  children_by_parent = Hash.new { |hash, key| hash[key] = [] }
 
  rows.each do |row|

Building a tree from flat rows in Ruby

recursion hash-grouping tree-structure
Intermediate 5 steps
php 
function memoize(callable $fn): callable
{
    $cache = [];
 

How memoization works in PHP closures

memoization closures higher-order-functions
Intermediate 8 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 
require 'json'
require 'set'
 
class SensitiveScrubber

Recursively scrubbing secrets from JSON

recursion data-masking pattern-matching
Intermediate 7 steps
python 
from pathlib import Path
 
 
def print_tree(root, prefix="", show_hidden=False):

Printing a directory tree with recursion

recursion filesystem sorting
Intermediate 6 steps
python 
from dataclasses import dataclass, fields, MISSING
from typing import get_type_hints, get_origin, get_args, Union
 
 

Type-checking dataclasses at runtime

dataclasses type-hints runtime-validation
Advanced 8 steps
typescript 
type CloneInput = Record<string, unknown> | unknown[] | Map<unknown, unknown> | Set<unknown>;
 
export function deepClone<T>(value: T): T {
  if (typeof structuredClone === "function") {

Building a deepClone with cycle safety

recursion deep-copy cycle-detection
Intermediate 8 steps
python 
from functools import wraps
 
 
def memoize(func):

Building a memoize decorator in Python

decorators closures memoization
Intermediate 5 steps
ruby 
module Fibonacci
  CACHE = Hash.new do |cache, n|
    cache[n] = cache[n - 1] + cache[n - 2]
  end

Memoizing Fibonacci with a Hash default block

memoization recursion hash-default
Intermediate 5 steps
java 
public final class BusinessDays {
 
    private BusinessDays() {
    }

Counting business days between two dates in Java

date arithmetic utility class streams
Intermediate 7 steps