Use feature testing to detect native Set,
and don't rely on `Set#to_h` which wasn't intended
as a public method.
https://github.com/ruby/psych/commit/
d58cff11af
@@ -23,7 +23,6 @@ require_relative 'psych/parser'
require_relative 'psych/omap'
require_relative 'psych/set'
require_relative 'psych/coder'
-require_relative 'psych/core_ext'
require_relative 'psych/stream'
require_relative 'psych/json/tree_builder'
require_relative 'psych/json/stream'
@@ -761,3 +760,5 @@ module Psych
self.domain_types = {}
# :startdoc:
end
+
+require_relative 'psych/core_ext'