recursive hash keys

recurse_keys.rb

# Returns keys from a hash recursively when that hash can contain hashes
# Handy for use with StrongParameters

recurse_keys = lambda do |h| h.inject([]) { |a, (k, v)| a << (v.is_a?(Hash) ? { k => recurse_keys.call(v) } : k) } rescue [] end

# Example
parms = {:foo=>:bar, :baz=>{:a=>:b, :c=>:d, :e=>:f}}
recurse_keys.call(parms)
# returns [:foo, {baz: [:a, :b, :c]}]

This would be handy for implementing strong_parameters permit! on certain keys as discussed here:

rails/rails#9454