From: M Mohr <messju@...>
Date: 2002-09-23T21:16:09+09:00
Subject: Re: String[#.]interpolate (was Re: String interpolation at will?)

"Hal E. Fulton" <hal9000@hypermetrics.com> writes:

> ----- Original Message ----- 
> From: "Hal E. Fulton" <hal9000@hypermetrics.com>
> To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> Sent: Friday, September 20, 2002 4:06 PM
> Subject: Re: String interpolation at will?
> 
> 
> > ----- Original Message ----- 
> > From: "Hal E. Fulton" <hal9000@hypermetrics.com>
> > To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> > Sent: Friday, September 20, 2002 3:30 PM
> > Subject: Re: String interpolation at will?
> > 
> > 
> > > Hmm, there have been times I wished for a String.interpolate
> > > method... couldn't be too hard to expose it. Wonder if it's
> > > worth it?
> > 
> > To reply to myself: I've just remembered why
> > this is nontrivial in pure Ruby. If you write 
> > a String#interpolate, it can't get to your
> > local variables, i.e. if you do:
> > 
> >   bar = "secret"
> >   foo = 'code is #{bar}'
> >   str = foo.interpolate
> > 
> > it won't work because #interpolate can't see
> > the bar variable. Hmm.
> > 
> > You can still do it outside of a method, of 
> > course.
> > 
> > I'm playing with a Proc now out of curiosity.
> 
> And to answer my own post again, I find that 
> this works OK.
> 
> Tempted to put ANN: on the subject line.  ;)
> 
> Code below. 
> 
> Cheers,
> Hal
> 
>   
>   # Let's make a setter for a class variable
>   class String
>     def String.interp=(blk)
>       @@interp = blk
>     end
>   end
>   
>   # Back to top-level scope
>   String.interp = (Proc.new do |s|
>     __str = s.dup
>     __str.gsub!(/"/,'\"')
>     eval('"' + __str + '"')
>   end)
>   
>   # Now define the methods
>   class String
>     def String.interpolate(str)
>       @@interp.call(str)
>     end
>     def interpolate
>       @@interp.call(self)
>     end
>   end
>   
>   # Now try it out
>   
>   str = <<'END'
>   He said, "I am the #{alpha} and
>   the #{omega}."
>   Have a nice day.
>   
>   END
>   
>   puts str
>   
>   alpha = "walrus"
>   omega = "weather is fine"
>   
>   str2 = str.interpolate
>   puts str2
>   
>   str3 = String.interpolate(str)
>   puts str3
>   
> And the output is:
> 
>   He said, "I am the #{alpha} and
>   the #{omega}."
>   Have a nice day.
> 
>   He said, "I am the walrus and
>   the weather is fine."
>   Have a nice day.
> 
>   He said, "I am the walrus and
>   the weather is fine."
>   Have a nice day.


very nice. but, unless i am missing something, there is just one flaw:
String.interp is always called in global context. you cannot use
String.interpolate inside a method and use local variables there.

have fun
messju