On Sep 30, 2011, at 4:32 PM, Srushti Ambekallu wrote:
> On 30/09/11 3:58 PM, David Chelimsky wrote:
>> On Sep 30, 2011, at 3:31 PM, Patrick J. Collins wrote:
>>
>>>> Proper usage, sure, but the memoization is only within each example - not
>>>> across examples. That way you can do this:
>>>>
>>>> let(:thing) { Thing.new }
>>>>
>>>> it "does something" do
>>>> thing.blah
>>>> thing.whatever
>>>> thing.yet_again
>>>> end
>>>>
>>>> In that case each reference to thing returns the same object.
>>>>
>>>> Make sense?
>>> Hmm.. now I am confused...
>>>
>>> What is the difference between:
>>>
>>> describe "Foo" do
>>>
>>> let(:foo) { Foo.new }
>>>
>>> it "is tubular" do
>>> foo.bar
>>> foo.baz
>>> end
>>>
>>> it "is gnarly" do
>>> foo.gnarl
>>> foo.wurd_up
>>> end
>>>
>>> end
>>>
>>> vs.
>>>
>>> describe "Foo" do
>>>
>>> before :each do
>>> @foo = Foo.new
>>> end
>>>
>>> it "seems just as tubular as the foo w/ let" do
>>> @foo.bar
>>> @foo.baz
>>> end
>>>
>>> it "seems just as gnarly as the foo w/ let" do
>>> @foo.gnarl
>>> @foo.wurd_up
>>> end
>>>
>>> end
>>>
>>> I am not seeing any difference...?
>> There is not, really, other than how the declaration of foo is expressed and
>> referenced. This evolved out of a common pattern in TDD:
>>
>> 1:
>>
>> describe "something" do
>> it "does something" do
>> thing = Thing.new
>> thing.do_something.should have_some_outcome
>> end
>> end
>>
>> 2:
>>
>> describe "something" do
>> it "does something" do
>> thing = Thing.new
>> thing.do_something.should have_some_outcome
>> end
>>
>> it "does something else" do
>> thing = Thing.new
>> thing.do_something_else.should have_some_other_outcome
>> end
>> end
>>
>> Now there is duplication so we can refactor out the declaration of thing. It
>> takes less work and is less error prone to change it to a let declaration
>> than to change the references to thing to an instance variable declared in a
>> before hook.
>>
>> Cheers,
>> David
>>
>> _______________________________________________
>> rspec-users mailing list
>> rspec-users@rubyforge.org
>> http://rubyforge.org/mailman/listinfo/rspec-users
>>
> One thing I noticed, and something that always catches me out is the fact
> that the 'let'ted object doesn't get instantiated until it gets referenced.
> Therefore,
>
> describe "all" do
> let(:foo) { Foo.create! }
>
> it "returns the created object" do
> Foo.all.should include(foo)
> end
> end
>
> ... fails, since at the time of calling :all, the 'foo' object hasn't been
> referred yet, and hence the block hasn't executed. "Foo.all" in the case
> above returns an empty array, which wouldn't have been the case with an
> instance object created in "before(:each)".
>
> Srushti
> http://c42.in
That's one of the benefits of let :) You can use it to declare objects but they
only get instantiated when you reference them.
See https://www.relishapp.com/rspec/rspec-core/docs/helper-methods/let-and-let
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