DigBang: Safely unsafe Ruby hash traversal

Here’s Hash#dig!, a handy little piece of code I wrote for a project. It’s similar to Ruby 2.3’s Hash#dig, but raises an exception instead of returning nil when a key isn’t found.

places = { world: { uk: true } }

places.dig  :world, :uk # true
places.dig! :world, :uk # true

places.dig  :world, :uk, :bvi # nil
places.dig! :world, :uk, :bvi # KeyError:
                              #   Key not found: :bvi

#dig is to #[] as #dig! is to #fetch

Ruby 2.3 introduces the new Hash#dig method for safe extraction of a nested value. It’s the equivalent of a safely repeated Hash#[].

#dig!, on the other hand, is the equivalent of a safely repeated Hash#fetch. It’s “safely unsafe” 😉 raising the appropriate KeyError anywhere down the line, or returning the value if it exists. This turns out to be very easy to implement in the functional style:

def dig!(*keys)
  keys.reduce(self) { |a, e| a.fetch(e) }

The full source code