From: Gavin Sinclair <gsinclair@...>
Date: 2004-09-09T09:47:14+09:00
Subject: Re: Q: Should String.upcase! work on a segment of a string?

Mike Hall wrote:
> Question: Should String.upcase! work on a segment of a string?
>
> 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.

>   > s[4..5] = s[4..5].upcase    # so, do it by-hand
>   => "ZZ"
>
>   > s				# and it's ok
>   => "AA11ZZ"

That's because of (psuedo-code)

  class String
    def []=(index, value)
      case index
      when Range then ...
      when Numeric then ...
      ...
      end
    end
  end

> Are there edge cases where this wouldn't be appropriate?

There's no way to make s[4..5].upcase! do what you suggest.

Cheers,
Gavin