From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2001-10-28T14:19:30+09:00
Subject: [ruby-talk:23666] Re: How to get a String to interpolate itself?

In article <FQLC7.13234$TF4.677798@sjcpnn01.usenetserver.com>,
Phil Tomson <ptkwt@shell1.aracnet.com> wrote:
>In article <3BDB73A2.7B1C14FF@path.berkeley.edu>,
> <vjoel@PATH.Berkeley.EDU> wrote:
>>Phil Tomson wrote:
>>> 
>
>It works, but it seems a bit kludgy.  Certainly not very OO.  It seems to 
>me that we need a String#interpolate method.
>str.interpolate => "This is the value of var: 3"
>

To critique mey own suggestion:
There probably is no 'interpolate' method defined for the String class 
because of the scoping problem: It would be interpolated in what context?

For example, let's say we define String#interpolate:
class String
  def interpolate
    eval "\"#{self.to_s}\""
  end
end

Now try:

var = 99
bstr = 'now try this: #{var}' 
bstr.interpolate

You'll get an error message about 'var' being an undefined variable - it's 
not defined with in the scope of String where it is being eval'ed.

So, in order to get it to work you would have to pass a binding in to the 
interpolate method:

class String
  def interpolate(bind)
    eval ("\"#{self.to_s}\"",bind)
  end
end
var = 99
bstr = 'now try this: #{var}'
p bstr.interpolate( binding()) 

Now it will work, but it's a bit nasty passing in the binding, couldn't 
there be some bad consequences of this? Any other ideas? (maybe we could 
just pass in a list of variables and their values to interpolate for).

Phil