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RedHanded

Wonder of the When-Be-Splat #

by why in bits

Well, okay, yes, we already know Ruby is expressive. And, if I know you, you’ll see a drop of awesomeness in:

 BOARD_MEMBERS = ['Jan', 'Julie', 'Archie', 'Stewick']
 HISTORIANS = ['Braith', 'Dewey', 'Eduardo']

 case name
 when *BOARD_MEMBERS
   "You're on the board!  A congratulations is in order." 
 when *HISTORIANS
   "You are busy chronicling every deft play." 
 end

I was refactoring a parser and it occured to me that I could just do a when *tokens.keys at one point. Ruby treats it just like a list of conditions. Consider Olympic ice dancing out-graced!

Addendum: I’m just gonna log a few of the other discoveries implied here, just to prove how handily this waxes if..include?’s sorry snout.

 case name when "Arthur", *BOARD_MEMBERS
   "Either you are a board member... or you are Arthur." 
 end

 case name when *BOARD_MEMBERS|HISTORIANS
   "We welcome you all to the First International
    Symposium of Board Members and Historians Alike." 
 end
23 Feb 2006 at 18:25 | 27 comments

yerejm

said on 23 Feb 2006 at 18:46

Say goodbye to include?, case. She wasn’t expressive enough.

Matt Todd

said on 23 Feb 2006 at 18:51

That’s beautiful! It communicated to me on three different levels! :-)

M.T.

humdrum

said on 23 Feb 2006 at 18:57

That is nicely expressive.. but why does it work?

Justin Palmer

said on 23 Feb 2006 at 19:02

Now thats aesthetics even a designer can love. :-)

andrew

said on 23 Feb 2006 at 20:22

Ruby’s case has a lot of goodness, but I never knew.

Danno

said on 23 Feb 2006 at 20:28

Beauti-tastic.

ConFused

said on 24 Feb 2006 at 00:04

That’s cool, but, as a newbie, I don’t see what it going on under the covers. Can someone explain it? Is this some kind of regexp matching?

Thanks!

why

said on 24 Feb 2006 at 00:05

humdrum: In times past, the splat has been used to pitch an array into a method as the method arguments:

 args = ["/tmp/a-gust-of-wind.txt", "w+"]
 open(*args) { |f| f << "..wchhoooo..." }

More recently, the splat is now widely used in place of to_a.

 animals = [:hound, :hawk]
 gopher = :gopher
 tigers = [:blue_tiger, :fierce_tiger]

 >> animals + [*gopher]
 => [:hound, :hawk, :gopher]
 >> animals + [*tigers]
 => [:hound, :hawk, :blue_tiger, :fierce_tiger]

So, juxtapose this with Ruby’s when statement which can take multiple conditions and you’ve got it.

 case obj
 when String, IO
   YAML.load obj
 else
   obj
 end

Joey__

said on 24 Feb 2006 at 03:21

Very nice, you learn something new every day!

By the way, you left off a ’ in front of Julie.

Thanks for the tip!

Josh

said on 24 Feb 2006 at 08:46 

JACKASS = ['phentermine']
case name
 when *JACKASS
   puts "You're a jackass spammer" 
 else 
   puts "Nothing to see here, move along" 
end

cilibrar

said on 24 Feb 2006 at 09:09

That was really awesome why. You never cease to amaze me!!!

why

said on 24 Feb 2006 at 15:45

Check. Sorry comments were defunct.

slumos

said on 24 Feb 2006 at 16:38

This should be a haiku, but I didn’t have time. With all the deep hacking and evil going on lately, I wonder if we’ve been distracted from the simple beauty of Ruby.

Cherry blossoms.

weeksie

said on 24 Feb 2006 at 20:00

It feels all pattern-match-y :)

Branstrom

said on 24 Feb 2006 at 22:43

“case name when” doesn’t feel all fuzzy inside, shouldn’t “when” be “is” for the first line? :p maybe im getting spoiled with all the english-simulating syntax otherwise around :p :p

tilman

said on 25 Feb 2006 at 03:47

This only works with Ruby 1.9, right?

WWWWolf

said on 25 Feb 2006 at 06:22

A programming language with a sane syntax? Will the the wonders this world has ever end!

Joey__

said on 25 Feb 2006 at 07:17

tilman:No, it works on Ruby 1.8.4, not sure about Ruby 1.8.2 though.

a=[1,2,3,4,4]

a.zip([a]) => [[1, [1, 2, 3, 4, 4]], [2, nil], [3, nil], [4, nil], [4, nil]]

a.zip([*a]) => [[1, 1], [2, 2], [3, 3], [4, 4], [4, 4]]

a.zip(*[a]) => [[1, 1], [2, 2], [3, 3], [4, 4], [4, 4]]

a.zip(a) => [[1, 1], [2, 2], [3, 3], [4, 4], [4, 4]]

sporkmonger

said on 25 Feb 2006 at 13:00

tilman: It works fine in 1.8.2 as well.


[1, *[2, 3, 4]]
=> [1, 2, 3, 4]

kode

said on 25 Feb 2006 at 17:09

I need to remember this. Might come in useful some time.

tilman

said on 26 Feb 2006 at 12:57

Mmh, the first example in the article doesn’t work for me on Ruby 1.8.4 :/

joey__

said on 26 Feb 2006 at 13:28

name has to be defined, you cannot copy and paste this code, it won’t work.

tilman

said on 27 Feb 2006 at 11:55

I’m not that stupid :P

Chuck

said on 27 Feb 2006 at 12:48

Works for me. What error are you getting?

joey__

said on 27 Feb 2006 at 16:59

tilman Its best to think of the most obvious things first :)

tilman

said on 28 Feb 2006 at 11:54

I just realized the result of the case expression was never written to stdout or something :o It works nicely if I add “puts” somewhere ;) tilman—

jvoorhis

said on 08 Mar 2006 at 20:14

Destructuring is delicious

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