From: Adam Keys <adam@...>
Date: 2005-04-22T22:34:33+09:00
Subject: Re: for .. in .. else?

Salutations,

On Apr 22, 2005, at 7:17 AM, David A. Black wrote:
> On Fri, 22 Apr 2005, Adam Keys wrote:
>
>> On Apr 21, 2005, at 5:46 PM, Hal Fulton wrote:
>>> FWIW I'll offer this (untested) alternative:
>>>  <table>
>>>    <tr><th>Songs</th></tr>
>>>    <% unless song_list.each do |song|%>
>>>      <tr><td><%= song.name %></td></tr>
>>>      <% end.empty? %>
>>>      <tr><td>no songs!</td></tr>
>>>    <% end %>
>>>    </tr>
>>>  </table>

Maybe I missed something, but when I extracted this code and ran it in 
irb, it didn't work like I thought it would:

irb(main):087:0> songs
=> ["Rocky Raccoon", "As My Guitar Gently Weeps", "She Came In Through 
The Bathroom Window"]
irb(main):088:0> unless songs.each do |song|
irb(main):089:2* p song
irb(main):090:2> end.empty?
irb(main):091:1> p 'no songs!'
irb(main):092:1> end
"Rocky Raccoon"
"As My Guitar Gently Weeps"
"She Came In Through The Bathroom Window"
"no songs!"
=> nil
irb(main):093:0>

The presence of 'no songs!' is not what I'd expected.
>
> Yours is different from Hal's, because in Hal's the iteration through
> the song list is sort of a side-effect of the testing of the
> condition, whereas you're just doing a standard chaining thing.  And
> you do create a temporary array :-)  (the return value of #reject)

This makes sense in isolation, however given the above result I'm 
curious as to what is actually going on.  As to the temporary variable, 
I am more tired of having "foo = []" all over my code.

> You could perhaps make it easier to read with a different formatting:
>
>   ary.reject {|e| e.some_predicate? } .each do |f|
>     f.do_something
>   end
>
> or something.  (Definitely lose the one-space indenting.)  If your
> friend still has trouble with it, buy him the Pickaxe :-)

I agree the {} block looks more like something that yields a value than 
do..end.  I think I had it that way at first but the line spilled over 
past column 80 so I changed it to a do...end, which I use when a block 
spans multiple lines.  Is that a common idiom or am I unique in this 
regard?

--
~akk
http://therealadam.com