# Append (\<\<) to Array attributes of DRb objects?

**URL:** <https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711>\
**Category:** Ruby\
**Created:** [July 30, 2007, 1:42am UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711 "2007-07-30T01:42:33Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 30, 2007, 1:42am UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/1 "2007-07-30T01:42:33Z")

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When working locally with an object whose attribute is meant to store  
an array, I have no problem making calls like:

object.items \<\< new\_item

If I try to do the same thing with a DRb object, though, appending has  
no effect on the remote object. I’ve distilled the problem down to  
this example…

My server:

require ‘drb’  
class TestServer  
attr\_accessor :items  
def initialize  
@items = []  
end  
def add\_item(item)  
@items \<\< item  
end  
def add  
sum = 0  
@items.each {|item| sum += item}  
sum  
end  
end  
server = TestServer.new  
DRb.start\_service(‘druby://localhost:9000’, server)  
DRb.thread.join

My client:

require ‘drb’  
DRb.start\_service()  
obj = DRbObject.new(nil, ‘druby://localhost:9000’)  
obj.items \<\< 1 #No effect.  
obj.items \<\< 2 #No effect.  
items = [1, 2]  
obj.items = items #Works.  
obj.add\_item(1) #Works.  
obj.add\_item(2) #Works.  
puts obj.add #Gives ‘6’ instead of ‘9’.

I’d rather my client programs be able to use append (\<\<) instead of an  
add\_item(item) method or direct assignment. How can I do this?

---

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 30, 2007, 1:54am UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/2 "2007-07-30T01:54:33Z")

</div>

Jay McGavren wrote:

> When working locally with an object whose attribute is meant to store  
> an array, I have no problem making calls like:
> 
> object.items \<\< new\_item
> 
> If I try to do the same thing with a DRb object, though, appending has  
> no effect on the remote object.

The #items method returns an Array. That Array is not DRbUndumped (i.e.,  
not a proxy object), so it gets _copied_ back to the client. Modifying  
that copy in the client can’t affect the original in the server.

Your #add\_item method is a good way around this.

Or, you could extend the array with DRbUndumped, to keep it on the  
server.

---

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 30, 2007, 1:58am UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/3 "2007-07-30T01:58:35Z")

</div>

Jay McGavren wrote:

> When working locally with an object whose attribute is meant to store  
> an array, I have no problem making calls like:
> 
> object.items \<\< new\_item
> 
> If I try to do the same thing with a DRb object, though, appending has  
> no effect on the remote object. I’ve distilled the problem down to  
> this example…

The BackgrounDRb mailing list will give you better odds of a good  
answer.

In general, I treat my background threads with the strictest isolation,  
and  
I don’t go passing arrays back and forth. Consider the marshalling that  
must  
occur just for one stinkin’ \<\<. So I don’t know the answer to your  
question,  
even though I have used BackgrounDRb on 2 projects so far…

---

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 30, 2007, 5:35pm UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/4 "2007-07-30T17:35:01Z")

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On 7/29/07, Phlip [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> The BackgrounDRb mailing list will give you better odds of a good answer.
> 
> In general, I treat my background threads with the strictest isolation, and  
> I don’t go passing arrays back and forth. Consider the marshalling that must  
> occur just for one stinkin’ \<\<. So I don’t know the answer to your question,  
> even though I have used BackgrounDRb on 2 projects so far…
> 
> –  
> Phlip

Note that he is not using BackgroundDRb, but DRb itself, so I believe  
this list is the most appropriate.

You should probably just extend the array with DRbUndumped, that will  
(IIRC) speed up the appending, and allow \<\< to work properly.

---

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 30, 2007, 10:36pm UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/5 "2007-07-30T22:36:54Z")

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On Jul 30, 8:33 am, “Chris C.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> You should probably just extend the array with DRbUndumped, that will  
> (IIRC) speed up the appending, and allow \<\< to work properly.

Thusly, yes?

Server:

require ‘drb’  
class UndumpedArray \< Array  
include DRbUndumped  
end  
class TestServer  
attr\_accessor :items  
def initialize  
@items = UndumpedArray.new  
end  
def add  
sum = 0  
@items.each {|item| sum += item}  
sum  
end  
end  
server = TestServer.new  
DRb.start\_service(‘druby://localhost:9000’, server)  
DRb.thread.join

Client:

require ‘drb’  
DRb.start\_service()  
obj = DRbObject.new(nil, ‘druby://localhost:9000’)  
obj.items \<\< 1  
obj.items \<\< 2  
puts obj.add #Gives ‘3’.

Seems to work pretty well. DRbUndumped may be the solution to my  
concerns about network overhead as well.

Thanks to everyone for the assistance!

-Jay

---

<div class="post-metadata">

**Author:** ![Jay\_McGavren](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e79b87/32.png) [@Jay\_McGavren](https://www.ruby-forum.com/u/Jay_McGavren)\
**Post date:** [July 31, 2007, 1:56am UTC](https://www.ruby-forum.com/t/append-to-array-attributes-of-drb-objects/110711/6 "2007-07-31T01:56:14Z")

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On Jul 30, 2007, at 13:35, Jay McGavren wrote:

> ```
> include DRbUndumped
> 
> ```
> 
> end  
> class TestServer  
> attr\_accessor :items  
> def initialize  
> @items = UndumpedArray.new

Get rid of UndumpedArray.

@items = Array.new  
@items.extend DRbUndumped