From: Jason Voegele <jason@...>
Date: 2002-09-26T20:51:50+09:00
Subject: Re: Const vs warning

J.Leuzinger wrote:

>Hi,
>Although a newbie, I am really impressed of this powerful and consistent
>language !
>Accidently I used the << operator instead of the + operator to concatenate
>two strings.
>The result was a bit surprising (but intelligibly if one uses the wrong
>method).
>What bothers me is that Ruby does not issue a warning when a Const String is
>modified by the << operator.
>If I use the += operator I get a warning.
>This seems to me a breach in terms of least surprise.
>Do I overlook something ?
>
When you create a constant in Ruby (by capitalizing the variable name) 
only the *reference* is constant, not the object it refers to.  That 
means that you will receive a warning if you attempt to make the 
reference refer to another object, but you are free to change the object 
that it is referring to:

CONST1 = 'Text1'
CONST1 = 'Text2'  # <- This will give warning

The << operator modifies a string in place, so it does not modify the 
reference to the string.  This is why you will not get a warning.  The 
+= operator, on the other, creates a new string that is a concatenation 
of its two operands, and then assigns the new string to the reference. 
 This is why you get a warning for += but not <<.

If you would like to make the string object itself  const, use freeze:

CONST1.freeze

This way you will not be able to modify the string.

-- 
Jason Voegele
"We believe that we invent symbols. The truth is that they invent us."
    -- Gene Wolfe, The Book of the New Sun