RSpec issue with Regex declared by let

foo.rb

class Foo
  def a_string
    "abcdef8"
  end
end

foo_spec.rb

require_relative "./foo"

describe Foo do
  let(:foo) {Foo.new}
  let(:my_matcher) {/^[a-z]+(\d)$/}

  it "should match and pass" do
    my_str = foo.a_string
    p my_matcher
    matcher = my_str.match(my_matcher)
    8.should == matcher[1].to_i
  end

  it "should also match and pass but fails" do
    my_str = foo.a_string
    #p my_matcher
    matcher = my_str.match(my_matcher)
    8.should == matcher[1].to_i
  end
end