From: Robert Klemme <shortcutter@...>
Date: 2012-12-24T21:13:22+09:00
Subject: Re: POLS and string-handling

On Mon, Dec 24, 2012 at 12:55 AM, Paul Magnussen <lists@ruby-forum.com> wrote:
> Thanks for all the replies.  I notice also that I can force changing of
> the value (as opposed to the reference) by substituting a trivial
> expression for the right-hand side of the assignment, e.g.
>
> # g) Expression
>
> myStringA = "Fred Shufflebotham"
> myStringB = myStringA + ""
> myStringB[0,4] = "Bert"
>
> => myStringA = "Fred Shufflebotham"
> => myStringB = "Bert Shufflebotham"
>
> But of course it's an utter kludge.  Is there really no more elegant
> way?

my_string_a = "Fred Shufflebotham"
my_string_b = my_string_a.dup

Note that in Ruby naming convention of local variables and method
names is not CamelCase but snake_case.

Paul, what you should take away from this discussion (I'll try to
summarize what other's have said already):

 - All variables hold _references_ to objects.*
 - Assignment copies an object reference and stores it in a variable.
 - String literals are really object constructors, i.e. they create a
new object whenever evaluated. (Don't worry, behind the scenes this is
made efficient.)
 - There are immutable classes (most numeric classes, nil,
TrueClass...) and mutable classes (all others including String).
 - Arithmetic operators return a reference to a new instance in order
to make math work properly (a + b + a would return wrong results if
the first + changed state of a and returned a reference to the mutated
a).

* Note that this is not completely true in terms of the
_implementation_ of MRI but it is true from the perspective of the
_language user_.

Kind regards

robert


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