module RSpec::Matchers

expect(5).not_to be_an_instance_of(Float)
expect(5).not_to be_an_instance_of(Numeric)
expect(5).to be_an_instance_of(Fixnum)

@example

Passes if actual.instance_of?(expected)

def be_an_instance_of(expected)
  BuiltIn::BeAnInstanceOf.new(expected)
end