From: Dmitry Bilunov <kmeaw@...>
Date: 2007-08-08T16:58:14+09:00
Subject: Re: non-constant strings

Skye Shaw!@#$ wrote:
> On Aug 7, 2:41 pm, Dmitry Bilunov <km...@kmeaw.com> wrote:
>>     if command.safe?
> This will result in a no method error, no?
It is just an example, assume that you have some safety-checking code 
here.

> Well, this is not the fault of the language, rather your SecureRunner
> class.
Yes, it is not fault of Ruby, I am just trying to understand, why do the 
strings work in a such way. Most operations can be done with immutable 
strings - an operation can return a new string, constructed from method 
caller and, optionally, arguments.

> This is the case any language where arguments are passed by reference.
>> but what is the reason Ruby has non-constant strings
> You mean mutable strings. Ruby does have constant strings:
> 
> irb(main):001:0> CONST="assbasscass"
> => "assbasscass"
> irb(main):002:0> CONST=123
> (irb):2: warning: already initialized constant CONST
> => 123
> 
> The String class wraps an array of chars, realloc()'in as necessary
> (ruby hackers correct me if I've mistakin).
Ruby string has array of chars, length (logical array size) and capacity 
(physical array size, probably larger, that logical) as Java's 
StringBuffer does.

> 
> Consider this in Java:
> 
> class SomeClassThatRequiredAlotOfTyping
> {
>   private StringBuffer sb
>   //....
>   public void printBuffer()  { System.out.println(sb); }
> }
> 
> StringBuffer sb = new StringBuffer("Dont Chnage!");
> 
> SomeClassThatRequiredAlotOfTyping clazz = new
> SomeClassThatRequiredAlotOfTyping(sb);
> // I'll show that private "read-only" var who's in charge!
> sb.delete(0,sb.length());
> sb.append("VB6, its ByVal keyword rocked... Not!");
> clazz.printBuffer();
> 
> Hope that helps.

But Java has also String, not just StringBuffer. Is there anything like 
String to protect a program against such things? Or some version of 
.freeze, which freezes a variable (field) to anyone, except instance 
methods?
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