Can anyone figure out what this block of ruby code does?

Question

Had this as part of an interview,I guessed it took incoming data, translated it into local language then commits to database? Which was obviously wrong.

def optimize(hsh)
  hsh.reduce({}) do |new_hsh, (k,v)|
    new_hsh[k.to_sym] = v.kind_of?(Hash) ? optimize(v) : v
    new_hsh
  end
end

Answer 1

It looks like it just recursively converts keys from nested hashes to symbols.

optimize({'k' => {'l' => 'v'}})
#=> {:k=>{:l=>"v"}}

Optimize is a poor name and each_with_object should be used instead of reduce :

def symbolize_keys(hash)
  hash.each_with_object({}) do |(k, v), new_hash|
    new_hash[k.to_sym] = v.is_a?(Hash) ? symbolize_keys(v) : v
  end
end

puts symbolize_keys('k' => { 'l' => 'v' })
#=> {:k=>{:l=>"v"}}

This method could be used to make sure that a nested hash has the correct keys. Some devs like to use string keys, others prefer symbols :

{'a' => 'b'}[:a]
#=> nil
symbolize_keys({'a' => 'b'})[:a]
#=> 'b'

Servers talk to each others with strings but Rails code is often written with symbols as keys. That's one of the reasons why HashWithIndifferentAccess exists.