Ruby keyword argument fun

keywords.rb

# A weird quirk of keyword args in Ruby that just tripped me up.
# An object passed as the second argument here will be used
# differently depending on its type.
def test(a, b = [], **c)
  [a, b, c]
end

# As expected, the default values work.
test(:one)           # => [:one, [], {}]
test(:one, :two)     # => [:one, :two, {}]

# But if the second arg is a hash, Ruby assumes we want to
# use it as the splatted keyword args. This feels odd to me.
test(:one, {})       # => [:one, [], {}]

# Even more confusing is that if Ruby thinks the second argument
# can be coerced into a hash, we get this mess...
class Foo
  def to_hash
    :oh_dear
  end
end
test(:one, Foo.new)  # => TypeError: can't convert Foo to Hash (Foo#to_hash gives Symbol)