Forum: Ruby What is meant by << operator ???

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Muhammad mohsin ali M. (Guest)
on 2009-01-10 21:07
What is meant by << operator?

For example this operator is used in following code,


/*****************************************************/
def add_product(product)
  current_item = @items.find {|item| item.product == product}
  if current_item
    current_item.increment_quantity
  else
    current_item = CartItem.new(product)
  @items << current_item
  end
  current_item
end
/*****************************************************/
Jan-Erik R. (Guest)
on 2009-01-10 21:12
(Received via mailing list)
Muhammad mohsin ali Ma schrieb:
>   else
>     current_item = CartItem.new(product)
>   @items << current_item
>   end
>   current_item
> end
> /*****************************************************/
it appends the object "current_item" to the Array @items
Muhammad mohsin ali M. (Guest)
on 2009-01-10 21:51
Do u know right syntax of form tag?
FrihD (Guest)
on 2009-01-10 22:30
(Received via mailing list)
Hello,

Muhammad mohsin ali Ma wrote:
> What is meant by << operator?

It is not an operator, but actually is the method "<<". So it depends on
the object that receives this method.

> def add_product(product)
>   current_item = @items.find {|item| item.product == product}
>   if current_item
>     current_item.increment_quantity
>   else
>     current_item = CartItem.new(product)
>   @items << current_item
>   end
>   current_item
> end

Consequently given that @items certainly is an Array, it appends
current_item to @items which seems quite intuitive.

--Lucas
Gary W. (Guest)
on 2009-01-10 23:04
(Received via mailing list)
On Jan 10, 2009, at 3:29 PM, FrihD wrote:
> Muhammad mohsin ali Ma wrote:
>> What is meant by << operator?
>
> It is not an operator, but actually is the method "<<". So it
> depends on the object that receives this method.


We just had a long rambling thread about operators vs. methods:
<http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/...
 >

I'd describe '<<' as a re-definable operator.  Syntactically it is an
operator but its semantics are defined by an associated method.

Ruby also has operators that can't be redefined:  || && or and not !  ?:

There are often semantics associated with operators that shouldn't be
disregarded without thought.  For example:

   lhs << rhs

often means that rhs will 'added' to lhs modifying lhs in the
process.  On the other hand:

   lhs + rhs

generally means new object formed by 'adding' rhs' to 'lhs' will be
returned and that lhs will not be modified.

Ruby doesn't enforce these semantics but developers shouldn't ignore
them either.

Gary W.
Tim G. (Guest)
on 2009-01-11 02:30
(Received via mailing list)
FrihD wrote:

> It is not an operator, but actually is the method "<<". So it depends
> on the object that receives this method.

Actually, it depends on what it depends on, because it's both (either
or).  It's a method, or just an operator (<< left shift bitwise
operator), or as an append operator.  I suppose it's all in the use and
wording, though.
David A. Black (Guest)
on 2009-01-11 02:42
(Received via mailing list)
Hi --

On Sun, 11 Jan 2009, Tim G. wrote:

> FrihD wrote:
>
>> It is not an operator, but actually is the method "<<". So it depends
>> on the object that receives this method.
>
> Actually, it depends on what it depends on, because it's both (either
> or).  It's a method, or just an operator (<< left shift bitwise
> operator), or as an append operator.  I suppose it's all in the use and
> wording, though.

The method-ness has a certain primacy, in the sense that this:

   a << b

is always a method call; that is, it is always the same as:

   a.<<(b)

The syntactic sugar, however, has the clear purpose of making it look
like an infix operator. I think it's an operator kind of the way
"attributes" are attributes -- that is, mainly in the eye of the
beholder. The language really doesn't care whether we call things
attributes and operators, so it's all about what helps people make
sense of it.


David

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Tim G. (Guest)
on 2009-01-11 03:46
(Received via mailing list)
David A. Black wrote:

>> or).  It's a method, or just an operator (<< left shift bitwise
>
> The syntactic sugar, however, has the clear purpose of making it look
> like an infix operator. I think it's an operator kind of the way
> "attributes" are attributes -- that is, mainly in the eye of the
> beholder. The language really doesn't care whether we call things
> attributes and operators, so it's all about what helps people make
> sense of it.
>
>
> David
>

That's pretty much what I was saying, too. (Or trying to say).  I
personally don't care how people refer to things, provided it conveys
the intent and function.  It's all good to me.
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