From: dblack@...
Date: 2007-01-13T08:55:26+09:00
Subject: Re: What does this mean? ||=

HI --

On Sat, 13 Jan 2007, Chris Gernon wrote:

> Justin Ko wrote:
>> I'm looking at this method and don't understand what ||= means:
>
> Much like 'x += 1' is a shortcut for 'x = x + 1', 'x ||= 1' is a
> shortcut for 'x = x || 1'.
>
> The significance of this is that the || method doesn't simply return a
> boolean value; it checks the first argument, returns it if it evaluates
> to 'true' (i.e. is something other than false or nil), and otherwise
> returns the second argument. So it's commonly used as a shortcut for an
> if/then statement, checking if the first argument is nil (or false). So
> the following are all equivalent:
>
> if @account
>  @account
> else
>  Account.find(session[:account_id])
> end
>
> is the same as:
>
> @account = @account || Account.find(session[:account_id])
>
> is the same as:
>
> @account ||= Account.find(session[:account_id])

Your first example doesn't set @account; it just tests it.  You'd need
to do the assignment explicitly:

   @account = if @account
                @account
              else
                Account.find(session[:account_id]
              end


David

-- 
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