Generates a method whose return value is memoized after the first call.
@example
describe Thing do let(:thing) { Thing.new } it "does something" do # first invocation, executes block, memoizes and returns result thing.do_something # second invocation, returns the memoized value thing.should be_something end end
# File lib/rspec/core/let.rb, line 22 def let(name, &block) define_method(name) do __memoized.fetch(name) {|k| __memoized[k] = instance_eval(&block) } end end
Just like let()
, except the block is invoked by an implicit
before
hook. This serves a dual purpose of setting up state
and providing a memoized reference to that state.
@example
class Thing def self.count @count ||= 0 end def self.count=(val) @count += val end def self.reset_count @count = 0 end def initialize self.class.count += 1 end end describe Thing do after(:each) { Thing.reset_count } context "using let" do let(:thing) { Thing.new } it "is not invoked implicitly" do Thing.count.should eq(0) end it "can be invoked explicitly" do thing Thing.count.should eq(1) end end context "using let!" do let!(:thing) { Thing.new } it "is invoked implicitly" do Thing.count.should eq(1) end it "returns memoized version on first invocation" do thing Thing.count.should eq(1) end end end
# File lib/rspec/core/let.rb, line 82 def let!(name, &block) let(name, &block) before { __send__(name) } end