Autovivifying hash - accessing a key automatically creates a hash at that key

gistfile1.rb

autovivifying = proc {|x| proc { Hash.new {|h,k| h[k] = x.call(x).call } } }.call(proc {|x| proc { Hash.new {|h,k| h[k] = x.call(x).call } } }).call

[53] pry(main)> autovivifying[:foo]
=> {}
[54] pry(main)> autovivifying[:foo][:bar]
=> {}
[55] pry(main)> autovivifying[:foo][:bar][:baz]
=> {}
[56] pry(main)> autovivifying
=> {:foo=>{:bar=>{:baz=>{}}}}