Regexp deconstruction keys to allow pattern matching

[zechris]

This is to allow Regexp matches in Ruby 2.7's new experimental Pattern Matching.

eg.

  case /(?<a>.)(?<b>.)/.match("xy")
  in a: "x", b:
    "a was 'x' and b was matched to #{b.inspect}"
  end

  #=> "a was 'x' and b was matched to 'y'"

MatchData#named_captures is close but not close enough as the Hash required from a deconstruct_keys() method that gets used during Pattern Matching requires symbolized keys.

NB. This is WIP as the C code hasn't actually been written yet...

Although, it could be used in the wild now with a refinement of MatchData like so:

module RegexpDeconstructKeys
  refine MatchData do
    # Temporary patch in ruby to make tests pass until the code gets re-written in C
    def deconstruct_keys(*keys)
      h0 = named_captures.transform_keys(&:to_sym)
      if keys
        keys = keys.flatten.compact
        raise TypeError unless keys.all? { |k| k.is_a?(Symbol) }
        h0 = h0.slice(*keys) unless keys.empty?
      end
      h0.inject({}) { |h, (k, v)| h[k] = v if v; h }
    end
    # Temporary patch in ruby to make tests pass until the code gets re-written in C
  end
end

using RegexpDeconstructKeys
case /(?<a>.)(?<b>.)/.match("xy")
in a: "x", b:
  puts "a was 'x' and b was #{b.inspect}"
end

#=> "a was 'x' and b was matched to 'y'"

(tested in ruby v2.7.1)
(see also - https://bugs.ruby-lang.org/issues/17036 )