How do I use the fetch method for nested hash?

Question

I have the following hash:

hash = {'name' => { 'Mike' => { 'age' => 10, 'gender' => 'm' } } }

I can access the age by:

hash['name']['Mike']['age']

What if I used Hash#fetch method? How can I retrieve a key from a nested hash?

As Sergio mentioned, the way to do it (without creating something for myself) would be by a chain of fetch methods:

hash.fetch('name').fetch('Mike').fetch('age')

Answer 1

From Ruby 2.3.0 onward, you can use Hash#dig:

hash.dig('name', 'Mike', 'age')

It also comes with the added bonus that if some of the values along the way turned up to be nil, you will get nil instead of exception.

You can use the ruby_dig gem until you migrate.

Answer 2

EDIT: there is a built-in way now, see this answer.

---

There is no built-in method that I know of. I have this in my current project

class Hash
  def fetch_path(*parts)
    parts.reduce(self) do |memo, key|
      memo[key.to_s] if memo
    end
  end
end

# usage
hash.fetch_path('name', 'Mike', 'age')

You can easily modify it to use #fetch instead of #[] (if you so wish).