From: Pau Garcia i Quiles <pgquiles@...>
Date: 2007-05-25T07:50:04+09:00
Subject: Re: Introducing the "it" keyword

Quoting dblack@wobblini.net:

> Hi --
>
> On Fri, 25 May 2007, Greg Fodor wrote:
>
>> A common pattern seen in a lot of ruby code is:
>>
>> g(m(x)) if/unless/while/until h(m(x))
>>
>> for example,
>>
>> puts "User: #{opts[:user]}" if opts[:user]
>> in this case, g(x) = puts "User: #{x}", h(x) = x, and m(x) =
>> opts[:user]
>>
>> or
>>
>> return v+1 if v +1 < 10
>> In this case, g(x) = x, h(x) = x < 10, and m(x) = v + 1
>>
>> This is obviously suboptimal code, as is, because it results in the
>> evaluation of m(x) twice. I propose a new keyword is added, "it",
>> which may appear within the statement to the left of the decorator.
>> So, the previous statements become:
>>
>> puts "User: #{it}" if opts[:user]
>>
>> and
>>
>> return it if |v + 1| < 10
>>
>> If and only if "it" is seen on the left hand side, the ruby
>> interpreter should store the expression result on the conditional into
>> a temporary storage and evaluate that as "it". It falls out of scope
>> after the statement. The use of pipes can designate a subexpression to
>> use for "it" instead (I don't have my heart set on pipes, but you get
>> the idea.)
>>
>> This keyword allows better DRY in ruby for this g(m(x)) op h(m(x))
>> pattern and also provides a nice optimization since your average lazy
>> programmer will usually evaluate m(x) twice instead of putting it into
>> temporary local storage themselves. By promoting it to a keyword, you
>> also prevent the problems seen here:   
>> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/166828
>>
>> Thoughts?
>
> I think something like 99% of all suggestions for changes to Ruby
> involve new punctuation -- which means that only a very tiny number of
> them can be accepted before Ruby turns into complete line noise.  So
> I'd not advocate the pipes version.  Maybe you could do:
>
>   return v + 1 if its < 10
>
> which of course is missing an apostrophe, speaking of punctuation :-)
> But something like that, maybe.

We are talking about semantic sugar here, so I don't think it's  
crucial. But why not try?

What about this less intrusive approach?

return v + 1 if < 10

Just omit entirely the subject and make operators assume the subject  
is what we "return".

-- 
Pau Garcia i Quiles
http://www.elpauer.org
(Due to the amount of work, I usually need 10 days to answer)