From: Robert Klemme <shortcutter@...>
Date: 2007-05-17T19:50:03+09:00
Subject: Re: Coopting String interpolation

On 17.05.2007 07:09, aurelianito wrote:
> 
> On 17 mayo, 01:33, Pe�a, Botp <b...@delmonte-phil.com> wrote:
>> # irb(main):005:0> greeting="hi, #{"Ms "+name.capitalize}"
>> # => "hi, Ms Aure"
>>
>> sorry, was too fast on the last example; should be..
>>
>> irb(main):006:0> greeting="hi, #{name="Anne";"Ms "+name.capitalize}"
>> => "hi, Ms Anne"
> 
> I'm trying to do some metaprogramming and I need to apply some
> operation to all the strings that are interpolated. But I can't change
> the interpolation. In the example, I would like that "hi, #{name}" to
> evaluate to "hi, AURE" instead of "hi, Aure". I know that inside the
> #{} "operator" I can put any ruby code, so "hi, #{name.capitalize}"
> would evaluate to what I want.
> 
> But I want it to execute code that I DON'T write there. Ideally, there
> should be a method hook or something to change the way the
> interpolation works. But I couldn't find it :(.  May be a different
> example may be more clear. How can I do to write to a file all the
> strings generated via interpolations (id est, all the strings that are
> generated evaluating the different #{} "operators" in a program)?

Frankly, it has not become clear to me what you are up to.  Can you 
maybe just state which problem you are trying to solve?

As for a solution to your original example, you can do something like 
this - but it's a hack and not very reliable:

class Env
   def initialize(vals)
     @vals = vals
   end

   def process(&b)
     instance_eval(&b)
   end

   def method_missing(s,*a,&b)
     super unless a.empty?
     @vals[s.to_sym].upcase
   end
end

irb(main):015:0> e=Env.new(:name=>'foo')
=> #<Env:0x7ff6d388 @vals={:name=>"foo"}>
irb(main):016:0> e.process { "bar #{name}" }
=> "bar FOO"
irb(main):017:0>

Kind regards

	robert