Ruby Language Hashes Automatically creating a Deep Hash
Example
Hash has a default value for keys that are requested but don't exist (nil):
a = {}
p a[ :b ] # => nil
When creating a new Hash, one can specify the default:
b = Hash.new 'puppy'
p b[ :b ] # => 'puppy'
Hash.new also takes a block, which allows you to automatically create nested hashes, such as Perl's autovivification behavior or mkdir -p:
# h is the hash you're creating, and k the key.
#
hash = Hash.new { |h, k| h[k] = Hash.new &h.default_proc }
hash[ :a ][ :b ][ :c ] = 3
p hash # => { a: { b: { c: 3 } } }
