How to specify Regexp options using Regexp.union

Question

In "How do I removing URLs from text?" the following code is suggested:

require 'uri'
#...
schemes_regex = /^(?:#{ URI.scheme_list.keys.join('|') })/i
#...

I tried to improve this to:

schemes_regex = Regexp.union(URI.scheme_list.keys)

but I can't figure out how the IGNORECASE option (i) should be specified.

Answer 1

I don't believe it's possible to pass option arguments to Regexp.union like that. You could of course specify them after the union operation:

require 'uri'

Regexp.new(Regexp.union(URI.scheme_list.keys).source, Regexp::IGNORECASE)
# => /FTP|HTTP|HTTPS|LDAP|LDAPS|MAILTO/i

Answer 2

schemes_regex = Regexp.union(
  *URI.scheme_list.keys
  .map{|s| Regexp.new(s, Regexp::IGNORECASE)}
)