From: anler hp <anlerhp@...>
Date: 2010-01-18T08:32:39+09:00
Subject: Re: What does ||= represent in this situation?

hello, the operator | | = is the same as the typical + =, -= and so  
on, why did exist in ruby and not in other languages is because in  
ruby any expression returns a value.
here is an example very closed but pretty much less effective in other  
language

a = false;
a || a = c;

this means, makes a = c only if a is falseš, same things happen with

a ||= c  -- equivalent to --> a = a || c (if a is false, the right  
side of the || will be evaluated and its value will be returned -this  
only happen in ruby-, so c is returned either true or false)

sorry for my english

> On Sun, Jan 17, 2010 at 11:31 AM, John Merlino <stoicism1@aol.com>  
> wrote:
>
>> Hey all, || is equal to Or. So what would ||= in this situation?
>>
>> def expensive
>> @expensive ||=
>> begin
>> n = 99
>> buf = ""
>> begin
>> buf << "#{n} bottles of beer on the wall\n"
>> # ...
>> n -= 1
>> end while n > 0
>> buf << "no more bottles of beer"
>> end
>> end
>>
>> Thanks for all suggestions. Also if you can interpret this, that  
>> would
>> be nice. What it appears here is an attempt of a do while loop.
>> --
>> Posted via http://www.ruby-forum.com/.
>>
>>
> This code is (presumably) showing that it is expensive to calculate  
> the
> string "99 bottles of beer on the wall\n98 bottles ... \n no more  
> bottles of
> beer" and so what it does instead is calculates the string the first  
> time
> the method is called, but then not again after that.
>
> The first time the method is called, @expensive will be nil, which  
> evaluates
> to false. So in the boolean expression, @expensive || "99  
> bottles ... " ,
> the string will be returned. The ||= command can be thought of as
> @expensive || ( @expensive = "99 bottles ... " )
>
> In this case, if @expensive does not have a value, it will assign  
> the string
> to it. After that, however, it will have the value, and so the  
> string will
> not be assigned to it. This is useful, because the code that  
> generates the
> string is expensive to perform, and so we will never perform it  
> unless we
> know we need it, and after it has been performed, it should not have  
> to be
> performed again.