Understand Any Code with Personalized Explanations

interface User {
  id: string;
  name: string;
  role: 'admin' | 'user';
}

const getUser = async (id: string): Promise<User> => {
  const response = await fetch(`/api/users/${id}`);
  return response.json();
};

from typing import Optional
from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    is_offer: Optional[bool] = None

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id}

@Service
public class UserService {
    private final UserRepository repository;
    
    public UserService(UserRepository repository) {
        this.repository = repository;
    }
    
    public Optional<User> findById(Long id) {
        return repository.findById(id);
    }
}

type Service struct {
    repo Repository
    cache Cache
}

func (s *Service) GetUser(ctx context.Context, id string) (*User, error) {
    if user, ok := s.cache.Get(id); ok {
        return user, nil
    }
    return s.repo.FindUser(ctx, id)
}

template<typename T>
class SmartPtr {
    T* ptr;
public:
    SmartPtr(T* p = nullptr) : ptr(p) {}
    ~SmartPtr() { delete ptr; }
    
    T& operator*() { return *ptr; }
    T* operator->() { return ptr; }
};

class User < ApplicationRecord
  has_many :posts
  validates :email, presence: true
  
  def self.find_active
    where(status: 'active')
      .includes(:posts)
      .order(created_at: :desc)
  end
end