From: Austin Ziegler <halostatue@...>
Date: 2004-09-10T04:52:57+09:00
Subject: Re: Q: Should String.upcase! work on a segment of a string?

On Fri, 10 Sep 2004 04:40:02 +0900, Mike Hall <mghallno@spamenteract.com> 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.

There's your conceptual error: there is no distinction of RHS and LHS.
There's a method, String#[]=, that is being used on the LHS when you
do:

  s[4..5] = s[4..5].upcase

So that's actually:

  s.__send__(:"[]="), 4..5, s[4..5].upcase)

String#[] returns a new object; String#[]= performs an indexed
assignment that is interpreted in String as replacing 4..5 with the
value provided.

-austin
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