Why is a string key for a hash frozen?

Question

According to the specification, strings that are used as a key to a hash are duplicated and frozen. Other mutable objects do not seem to have such special consideration. For exa

Answer 1

See this thread on the ruby-core mailing list for an explanation (freakily, it happened to be the first mail I stumbled across when I opened up the mailing list in my mail app!).

I've no idea about the first part of your question, but hHere is a practical answer for the 2nd part:

  new_hash = {}
  h.each_pair do |k,v|
   new_hash.merge!({k.downcase => v}) 
  end

  h.replace new_hash

There's lots of permutations of this kind of code,

  Hash[ h.map{|k,v| [k.downcase, v] } ]

being another (and you're probably aware of these, but sometimes it's best to take the practical route:)