From: Markus <markus@...>
Date: 2004-09-10T04:54:52+09:00
Subject: Re: Q: Should String.upcase! work on a segment of a string?

On Thu, 2004-09-09 at 12:40, Mike Hall wrote:
> Gavin Sinclair  wrote:
> 
> 
> >> We can assign to a sub-string, so I thought that a bang-method might
> >> also work on a sub-string.
> 
> >>   s = 'AA11zz'		# define a string
> >>
> >>   > s[4..5].upcase!		# try to change part of it
> >>   => "ZZ"			# yeah, ok, the new string is changed,
> >> but...
> >>   > s
> >>   => "AA11zz"		# the original string wasn't affected
> >
> >s is one object; s[4..5] is another.  What you do to the second object is
> >none of the first's business.
> 
> I don't understand that... we can outright assign to the substring and it _does_ affect the original string.
> 
> I agree that pulling out s[4..5] (using it on the RHS) will give me a new object, that's cool.  
> 
> But -- if the string range reference is on the LHS, then it refers to a segment of 's', not some new object.  That's what I'm after.  If s.upcase! affects s, then it would be cool if s[4..5].upcase! also affected (a portion) of s.
> 
> But it doesn't, and I guess it won't.  
> OK.  Thanks, everyone!
> 

DON'T TRY THIS TRICK AT HOME

It is possible to do what you are asking, but I seriously doubt it is
worth the trouble.  A sketch (NOT a complete or robust implementation):

class String
    alias at  []
    def [](arg)
        case arg
          when Range then A_magic_substring.new(self,arg)
          else at(arg)
          end
        end
    end

class A_magic_substring
   attr_reader :host,:loc
   def initialize(h,l)
       @host = h
       @loc  = l
       end
   def upcase!
       @host[@loc] = @host.at(@loc).upcase
       end
   def to_str
       @host.at(@loc)
       end
   def to_s
       to_str
       end
   def inspect
       to_str
       end
   end

s = "My string"
p s
p s[3..5]
s[3..5].upcase!
p s