From: Erik Michaels-Ober <sferik@...>
Date: 2009-08-10T04:19:43+09:00
Subject: Making Hash a first-class citizen

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I've noticed a couple inconsistencies in the way Ruby hashes are treated
(compared to, say, arrays).  While I've been able to monkey-patch solutions,
I thought I would bring these inconsistencies to the attention of the group
with they hope that they might be resolved in a future version of the
language, which I love dearly.

For starters, there's no to_hash method on nil.  This causes a problem when
I want to call an instance method on an object that may or may not be nil
(for example, a hash of parameters from an HTTP request).

A common way to avoid a NoMethodError is by casting an object to a
particular type before calling a method on it.  For example:

string_or_nil.to_s.capitalize

This technique can be used for arrays, floats, integers, and strings.  It
would seem to follow that I could do the same for hashes:

hash_or_nil.to_hash.rehash

but instead I must do something like this:

(hash_or_nil || nil).rehash

or patch NilClass like this:

class NilClass
  def to_hash
    {}
  end
end

which seems to me like it shouldn't be necessary for a "primitive" type.


Second, I would argue that there should be + (plus), - (minus), and &
(ampersand) methods on hashes, that function the same way they do for arrays
(concatenation, difference, and intersection, respectively).

These few changes would go a long way toward making Hash a first-class
citizen in Ruby.

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