# Dependency injection with Needle gem

**URL:** <https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322>\
**Category:** Ruby\
**Created:** [April 9, 2008, 8:40pm UTC](https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322 "2008-04-09T20:40:52Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![cremes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e19b73/32.png) [@cremes](https://www.ruby-forum.com/u/cremes)\
**Post date:** [April 9, 2008, 8:40pm UTC](https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322/1 "2008-04-09T20:40:52Z")

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I am puzzling through a few things with needle and dependency  
injection. I only know of one library that uses it which is net-ssh (v  
1.1.2) since both were written by Jamis B…

Anyone know of another publicly available gem (or two) that uses  
needle for dependency injection? The more examples I have the easier  
it will be for me to figure out my development issues.

Thanks…

cr

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**Author:** ![cremes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e19b73/32.png) [@cremes](https://www.ruby-forum.com/u/cremes)\
**Post date:** [April 9, 2008, 10:45pm UTC](https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322/2 "2008-04-09T22:45:23Z")

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On Apr 9, 12:39 pm, Chuck R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> I am puzzling through a few things with needle and dependency  
> injection. I only know of one library that uses it which is net-ssh (v  
> 1.1.2) since both were written by Jamis B…
> 
> Anyone know of another publicly available gem (or two) that uses  
> needle for dependency injection? The more examples I have the easier  
> it will be for me to figure out my development issues.

DI has no place in Ruby. So says Jamis B. himself:

[http://weblog.jamisbuck.org/2007/7/29/net-ssh-revisited](http://weblog.jamisbuck.org/2007/7/29/net-ssh-revisited)

“I’ve since learned my lesson and have come to understand that  
although DI is a nifty technique that works well in some environments,  
it is wholly unnecessary in Ruby. Ruby sports an agility that Java  
will never know, and can get by without such crutches.”

Regards,

Dan

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**Author:** ![cremes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e19b73/32.png) [@cremes](https://www.ruby-forum.com/u/cremes)\
**Post date:** [April 9, 2008, 10:48pm UTC](https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322/3 "2008-04-09T22:48:24Z")

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Chuck,  
I originally started out using needle for my DI for a game I’m writing  
in  
ruby. However, someone showed me DIY that I like a little better  
Your object dependencies are mapped out in a yaml file. It might be  
something worth checking out:  
[http://rubyforge.org/projects/atomicobjectrb/](http://rubyforge.org/projects/atomicobjectrb/)

/Shawn

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**Author:** ![cremes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e19b73/32.png) [@cremes](https://www.ruby-forum.com/u/cremes)\
**Post date:** [April 9, 2008, 11:52pm UTC](https://www.ruby-forum.com/t/dependency-injection-with-needle-gem/134322/4 "2008-04-09T23:52:29Z")

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On Wed, Apr 9, 2008 at 4:44 PM, Daniel B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> DI has no place in Ruby. So says Jamis B. himself:
> 
> [Buckblog: Net::SSH revisited](http://weblog.jamisbuck.org/2007/7/29/net-ssh-revisited)
> 
> “I’ve since learned my lesson and have come to understand that  
> although DI is a nifty technique that works well in some environments,  
> it is wholly unnecessary in Ruby. Ruby sports an agility that Java  
> will never know, and can get by without such crutches.”

There’s a difference between dependency injection the pattern, and  
dependency-injection tools/frameworks.

It’s still a good idea to write classes that have their collaborators  
passed in, rather than finding or creating them internally.

One of my favorite examples:

# 1. Not so great

class Whatsit  
def initialize  
@timestamp = Time.now  
end  
end

# 2. better

class Whatsit  
def initialize(clock=Time)  
@timestamp = clock.now  
end  
end

#2 is better because it’s decoupled from the nondeterministic system  
clock, and thus easier to test.

Sure, with ruby Mock Object libraries you can do things like:

Time.stub!(:now).and\_return(“TIMESTAMP”)

…but this runs the risk of breaking unrelated code that also happens  
to be called in the test. And no, that’s not a theoretical risk;  
I’ve had real tests fail because I needed to deterministically test  
time-based code and some other code (like, say, RSpec itself) depended  
on Time.now.

DI frameworks may be overkill in Ruby, but DI is still a good way of  
breaking up your dependencies and keeping things decoupled.

–  
Avdi

Home: [http://avdi.org](http://avdi.org)  
Developer Blog: [http://avdi.org/devblog/](http://avdi.org/devblog/)  
Twitter: [http://twitter.com/avdi](http://twitter.com/avdi)  
Journal: [http://avdi.livejournal.com](http://avdi.livejournal.com)