Oh but that's not a minor correction at all :-) The fact that it's b === a
rather than a === b is all-important here, and if I had thought about it
that way round, things might have been clearer to me in the first place,
because I would have been forced to consider what kind of an object the
proc was so that it could usefully call its === method. In looking at what
it would return I was getting ahead of myself, much as I sometimes do when
looking at JavaScript functions-that-return-functions.
I would have thought that "yields" was exactly the right computer-sciencey
term here. What would you suggest instead?
I just went and tried handing an object to a C++ switch statement. Why had
I never thought of doing this before, I wondered? Can't be done. Illegal
switch expression. Case expression not constant. Doh! Ruby 1, C++ 0.
On Friday, August 1, 2014 10:09:29 PM UTC+10, Dave Burt wrote:
>
> Hi Mark,
>
> First a minor correction: "case a when b ..." is actually "if b === a ..."
> -- the === method is called on object b with argument a.
>
> "yields" is not a clear word to use -- in Ruby it refers to a method
> calling a passed block.
>
> But you're right, you have misunderstood what proc returns. The proc
> method returns a Proc object, and "Proc objects are blocks of code." The
> Proc object in your example accepts an argument, calls its "more_blue?"
> method, and returns the result. That result will be true or false, but the
> Proc is a essentially function which can be called.
>
> Then, also, the Proc has a === method. case...when turns into if like this:
>
> if (proc { |color| color.more_blue? }) === color
> "blueish"
>
> Proc#=== returns the result of the Proc when called with the case subject.
> So to run that when clause, the proc will be called with the color as
> argument, equivalent to this if statement:
>
> if (proc { |color| color.more_blue? }).call(color)
> "blueish"
>
> http://www.ruby-doc.org/core-2.1.1/Kernel.html#method-i-proc
> http://www.ruby-doc.org/core-2.1.1/Proc.html.
>
> Chris Pine wrote a great intro to blocks and procs in Ruby over a decade
> ago now, which includes some exercises to play with and cement your
> understanding:
> https://pine.fm/LearnToProgram/?Chapter=10
>
> Cheers,
> Dave
>
>
> On Fri, Aug 1, 2014 at 6:01 PM, Marky Mark <[email protected] <javascript:>
> > wrote:
>
>> Um, I just wrote my original question out and stared at it some more and
>> realised it was a stupid question to begin with :-(
>>
>> But the more I think about it the more I'm confused (and maybe this is
>> where hearing what Tim said at the time would help).
>>
>> Conceptually I see "case a when b ... when c ... else ..." as being the
>> same as "if a === b ... elsif a === c ... else ..." (as indeed slides 67-69
>> show) but that seems to fail for slide 62's use of proc:
>>
>> case color
>> when proc { |color| color.more_blue? }
>> "blueish"
>>
>> because comparing color with what the proc yields (true or false) surely
>> doesn't work. Am I misunderstanding what proc yields?
>>
>>
>> On Friday, August 1, 2014 5:08:06 PM UTC+10, Dave Burt wrote:
>>
>>> Thanks for the notes, Tim!
>>>
>>> Mark, post your case questions here!
>>>
>>> On the same topic, here is an article by Why on another feature of
>>> Ruby's case statements: you can *splat* an array like this:
>>>
>>> foo = 3
>>> ARRAY = [/abc/, Hash, 1..5]
>>> case foo; when *ARRAY; 'included'; else "doesn't === anything in the
>>> array"; end
>>>
>>> http://viewsourcecode.org/why/redhanded/bits/wonderOfTheWhenBeFlat.html
>>>
>>> Cheers,
>>> Dave
>>>
>>>
>>> On Fri, Aug 1, 2014 at 2:53 PM, Marky Mark <[email protected]> wrote:
>>>
>>>> Just slides though, no soundtrack? Familiar with case statements as I
>>>> am in general, I can't help thinking I'm missing a little of the
>>>> subtlety/reasoning w.r.t Ruby. I do have one or two stupid questions.
>>>> Should I post here or ask you privately?
>>>>
>>>>
>>>> On Thursday, July 31, 2014 3:04:32 PM UTC+10, Tim Moore wrote:
>>>>>
>>>>> Yes, I'll echo Dave's thoughts: thanks to the organisers and the
>>>>> substitute host!
>>>>>
>>>>> My slides are up at https://speakerdeck.com/tim
>>>>> moore/rubys-magical-case-statement and http://www.slideshare.net/
>>>>> timothymoore/rubys-magical-case-statement (take your pick)
>>>>>
>>>>> On Thursday, July 31, 2014 8:52:42 AM UTC+10, Dave Burt wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Thanks to the organisers and speakers for another great evening.
>>>>>>
>>>>>> May I ask again for links to any of the talks that are available?
>>>>>>
>>>>>> I think Duncan referenced his Github repo https://github.com/duncan
>>>>>> -bayne/presentations
>>>>>>
>>>>>> Cheers,
>>>>>> Dave
>>>>>>
>>>>>>
>>>>>> On Fri, Jul 25, 2014 at 1:17 PM, Mario Visic <[email protected]>
>>>>>> wrote:
>>>>>>
>>>>>>> Hi All
>>>>>>>
>>>>>>> The Melbourne Ruby meet will be happening next wednesday evening
>>>>>>> (the 30th July), with our usual array of entertaining talks, delicious
>>>>>>> food, tasty beverages, and delightful company (that’s you!).
>>>>>>>
>>>>>>> WHEN: Wednesday 30th July, arrive at 6pm for a 6:30pm start,
>>>>>>> wrapping up around 9pm.
>>>>>>> WHERE: Inspire9, Level 1, 41-43 Stewart Street
>>>>>>> WHAT: Three speakers, plus socialising, good food (not pizza) and
>>>>>>> drinks.
>>>>>>>
>>>>>>> Our line-up this month is:
>>>>>>> Jordan Lewis + Luke Arndt - Styleguide driven development
>>>>>>> Duncan Bayne - There’s no such thing as magic - tools and techniques
>>>>>>> for Ruby developers
>>>>>>> Tim Moore - Case Statements and ===
>>>>>>>
>>>>>>> All of these details are repeated on Meetup, for those who prefer
>>>>>>> that as their source of event information:
>>>>>>> http://www.meetup.com/Ruby-On-Rails-Oceania-Melbourne/events
>>>>>>> /175705562/
>>>>>>>
>>>>>>> Yet again, food is sponsored by Envato, Lookahead Search and
>>>>>>> Redbubble, the drinks by Zendesk, and the space by Inspire9.
>>>>>>>
>>>>>>> If you've any questions or thoughts, get in touch - we're looking
>>>>>>> forward to seeing you all there :)
>>>>>>>
>>>>>>> --
>>>>>>> Mario & Pat
>>>>>>>
>>>>>>> --
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>>>>>>>
>>>>>>
>>>>>> --
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>>>
>>>
>
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