let vs def

1_let.rb

desc "A user's comment" do
  let(:user) { User.create! name: "John" }
  let(:comment) { user.comments.create! }

  it "delegates to user's name" do
    comment.name.should eq(user.name)
  end
end

2_def.rb

desc "A user's comment" do
  def user
    @user ||= User.create! name: "John"
  end

  def comment
    @comment ||= user.comments.create!
  end

  it "delegates to user's name" do
    comment.name.should eq(user.name)
  end
end

3_def_condensed.rb

desc "A user's comment" do
  def user; @user ||= User.create! name: "John"; end
  def comment; @comment ||= user.comments.create!; end

  it "delegates to user's name" do
    comment.name.should eq(user.name)
  end
end