From: Brian Candler <b.candler@...>
Date: 2009-01-22T06:57:57+09:00
Subject: Re: String doesnt auto dup on modification

RK Sentinel wrote:
> Anyway, through trial and error, I start dup()'ing strings myself. I am
> aware of freeze().
> 
> But would like to know how others handle this generally in large apps.
> 
> - Do you keep freezing Strings you make in your classes to avoid
> accidental change
> 
> - Do you habitually dup() your string ?

Generally, no.

Of course there is no contract to enforce this, but in many cases it 
would be considered bad manners to modify an object which is passed in 
as an argument.

If you only read the object, then it doesn't matter. If you need a 
modified version, create a new object. Usually this doesn't require 
'dup'.

  def foo(a_string)
    a_string << "/foo"            # bad
    a_string = "#{a_string}/foo"  # good
    a_string = a_string + "/foo"  # good
  end

  DEFAULT_OPT = {:foo => "bar"}

  def bar(opt = {})
    opt[:foo] ||= "bar"           # bad
    opt = DEFAULT_OPT.merge(opt)  # good
  end

If you are paranoid, you can freeze DEFAULT_OPT and all its keys and 
values.

Sometimes you will see frozen strings as an optimisation to reduce the 
amount of garbage objects created:

  ...
  foo["bar"]        # creates a new "bar" string every time round

  BAR = "bar".freeze
  ...
  foo[BAR]          # always uses the same object

This probably won't make any noticeable difference except in the most 
innermost of loops.
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