From: Joel VanderWerf <vjoel@...>
Date: 2003-01-22T07:41:53+09:00
Subject: Re: Overloading operators

Dmitri Colebatch wrote:
> I was also wondering if there is a way to implement +=
> 
>   total = Amount.aud(300)
>   total += Amount.aud(500)
> 
>   total -> AUD 800

No need, since "x += y" is just syntax for "x = x + y". Once you define 
#+, youve got "+=" as well.

But this may not be what you want, if your #+ method returns a *new* 
instance, and you would rather increment the object that total refers to.

In that case, you may want an #increment method and use it like:

  total.increment Amount.aud(500)

Or you could define #<< to do the same thing:

   total << Amount.aud(500)

The key point is that these two methods operate destructively on the 
object referred to by the local variable total, whereas += assigns a new 
object to that variable.