From: Robert Klemme <shortcutter@...>
Date: 2008-09-12T20:09:13+09:00
Subject: Re: pass by reference in each loop

2008/9/12 Xiong Chiamiov <xiong.chiamiov+ruby_forum@gmail.com>:
> Robert Klemme wrote:
>> 2008/9/12 Xiong Chiamiov <xiong.chiamiov+ruby_forum@gmail.com>:
>>>> That's quite near to what I suggested: just drop all the @a, @b etc. and
>>>> stuff everything in an array - or have multiple arrays, one per class of
>>>> data (i.e. data which undergoes wml and data which does not).  Anyway,
>>>> chances are that you'll be able to find an elegant solution without
>>>> needing to change the language.
>>>
>>> I don't think I understood what you were suggesting the first time.  If
>>> I understand what you're suggesting, it is to have the values themselves
>>> in the array, rather than variables pointing *to* those values, yes?
>>
>> What exactly do you mean by "variable pointing to those values"?
>
> Well, I'm not quite sure how to explain it.  I think you cleared up what
> I was thinking right after this part, though:
>
> Robert Klemme wrote:
>> The value
>> (object) does not care how many references are around pointing to it.
>> With
>>
>> @x = Object.new
>> @y = Object.new
>> @a = [@x, @y]
>>
>> and
>>
>> @a = [Object.new, Object.new]
>>
>> there is no difference with regard to array contents.
>
>> Yep.  Problem is, you present just a very tiny piece of your
>> application so it is extremely hard for use to suggest an appropriate
>> solution.
>
> Ah, I knew I had part of it online somewhere:
> http://production.xyztextbooks.com/wml.php/generator .  This is the PHP
> version (before I converted it to Rails), so it hasn't had the benefit
> of some bugfixes and such, but you can at least *see* what I'm talking
> about.
>
> This page (http://production.xyztextbooks.com/wml.php/generator/syntax)
> has some of the basic syntactical things for this.  Essentially, there
> is an application called Webwork that uses a special dialect of Perl
> intermingled with Tex, and I'm created a front-end to problem-creation,
> which normally involves writing code that most teachers are not
> comfortable with (see http://webwork.maa.org/wiki/SampleProblem1).
>
> So then, it's just a simple form (using form_tag, I believe), and I grab
> all of the request parameters at the top of the script.  The question,
> answer and answer_explanation all need to be run through a method that
> parses the wml (as I'm calling it) into Perl/Tex code appropriate for
> the problem, for instance, from ==3/5== to \(frac{3}{5}\).
>
> As you can see, it's currently only those three fields that I need to
> parse; I don't want to use extra resources running everything through
> parsing.  In the future, though, I see a larger number of fields that
> need to be parsed, which is what I'm trying to write for.

So, one way to do it would be this:

class WhateverYouNameIt
  NEEDS_PARSING = [
    :foo,
    :bar,
  ]

  def initialize
    @inputs = {}
  end

  # code that fetches input from somewhere

  def parse
    NEEDS_PARSING.each do |label|
      @inputs[label] = wml(@inputs[label])
    end
  end
end

But then again, whether this approach is better ultimately depends on
- as I said - whether you more often than not need to treat those
inputs uniformly.  This I cannot know and in case you are not, then
I'd just plain write the statements in code with all variables, i.e.

@foo = wml(@foo)
@bar = wml(@bar)

even if it looks tedious.  Verbosity can be better at times because it
makes things clearer.

Cheers

robert

-- 
use.inject do |as, often| as.you_can - without end