From: David Masover <ninja@...>
Date: 2008-08-20T14:00:28+09:00
Subject: Re: Immutable, Interned strings??

On Monday 18 August 2008 05:10:58 Mayuresh Kathe wrote:
> Hello,

> What is the meaning of immutable, interned strings?
> Would like to know in common, general English :-)

Others have explained, mechanically. In terms of usage, you would use this in 
at least a few places you might otherwise use an Enum or a global constant in 
other languages.

For example, suppose you have a function which can do three slightly different 
things. Say, for the sake of argument, it generates an input field, which can 
be a checkbox, a dropdown, or a text field. You could call it like this:

field :checkbox
field :dropdown
field :text

And the function might look like this:

def field(type)
  # do some stuff common to all types
  if type == :checkbox
    # do something special for the checkbox
  end
  # more common stuff...

... you get the idea.

And yes, they're used widely as hash keys -- in particular, to make up for the 
fact that Ruby doesn't have named arguments.

But if you want to know how that works, just look at any Rails example code:

has_many :accounts, :through => :customers

It's that last bit that's interesting, because you could always decide that 
you don't want customers. You want zebras:

has_many :zebras, :class => 'Customer'
has_many :stripes, :through => :zebras, :class => 'Account'

I don't know if that will actually work, but you get the idea.