# New gem for instantiating nested objects

**URL:** <https://www.ruby-forum.com/t/new-gem-for-instantiating-nested-objects/107659>\
**Category:** Ruby\
**Created:** [June 24, 2007, 10:48pm UTC](https://www.ruby-forum.com/t/new-gem-for-instantiating-nested-objects/107659 "2007-06-24T22:48:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Craig\_Muth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ec9cab/32.png) [@Craig\_Muth](https://www.ruby-forum.com/u/Craig_Muth)\
**Post date:** [June 24, 2007, 10:48pm UTC](https://www.ruby-forum.com/t/new-gem-for-instantiating-nested-objects/107659/1 "2007-06-24T22:48:57Z")

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Chris C. and I threw together a simple gem to help create nested  
hierarchies (without relying on constructors). Sample usage:

require ‘lay’  
car = Car.lay( :color =\> “Red”, :driver =\> Driver.lay( :name =\> “Bob”  
) )

Is anyone aware of something out there that already does this (in Ruby)?

Note that in the above example Car and Driver might not have  
constructors  
defined. As you’ve probably guessed the example simply instantiates a  
Car,  
sets its ‘color’ attr to “Red”, and sets its ‘driver’ attr to a new  
Driver  
instance (whose ‘name’ attr is set to “Bob”).

The idea was largely borrowed from groovy. I’ve used the groovy way of  
doing this extensively and have found it to be particularly useful in  
test  
cases, when you need to construct nested objects to use as test input.

Please let us know if we’re reinventing the wheel. Otherwise, please do  
a  
“gem install lay” and try it out and give us feedback if you think it  
might  
be useful to you.

Other features:

- Also pass parameters to constructors
  - Car.lay( [“Jetta”, “V6”], :color =\> “Red” )

- Set member vars that don’t have attr’s defined
  - Car.lay( :\_color =\> “Red” )
  - This sets the @color member variable
  - We should probably change it to use :@color instead of :\_color

–Craig

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<div class="post-metadata">

**Author:** ![Craig\_Muth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ec9cab/32.png) [@Craig\_Muth](https://www.ruby-forum.com/u/Craig_Muth)\
**Post date:** [June 25, 2007, 7:29am UTC](https://www.ruby-forum.com/t/new-gem-for-instantiating-nested-objects/107659/2 "2007-06-25T07:29:04Z")

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Craig Muth wrote:

> Chris C. and I threw together a simple gem to help create nested  
> hierarchies (without relying on constructors). Sample usage:
> 
> require ‘lay’  
> car = Car.lay( :color =\> “Red”, :driver =\> Driver.lay( :name =\> “Bob” ) )

There looks to be overlap with Mocha  
([http://mocha.rubyforge.org/classes/Mocha/AutoVerify.html#M000005](http://mocha.rubyforge.org/classes/Mocha/AutoVerify.html#M000005)),  
though, judging from your “Other features” section, not 100%.

---

<div class="post-metadata">

**Author:** ![Craig\_Muth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ec9cab/32.png) [@Craig\_Muth](https://www.ruby-forum.com/u/Craig_Muth)\
**Post date:** [June 25, 2007, 7:53pm UTC](https://www.ruby-forum.com/t/new-gem-for-instantiating-nested-objects/107659/3 "2007-06-25T19:53:15Z")

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> There looks to be overlap with Mocha  
> ([http://mocha.rubyforge.org/classes/Mocha/AutoVerify.html#M000005](http://mocha.rubyforge.org/classes/Mocha/AutoVerify.html#M000005)),  
> though, judging from your “Other features” section, not 100%.

Thanks for the tip.

I might have overlooked something but it seems the overlap is more in  
application than in functionality (meaning they differ functionally but  
can  
both be applied to creating objects for test cases). The lay() method  
creates instances of the target class and sets its attr’s, whereas it  
looks  
like Mocha’s stub and mock methods create anonymous objects, or modify  
or  
add methods to existing classes/objects.

The lay() method can be fairly useful outside of test cases, as a  
shorthand  
for constructing objects that don’t have convenient constructors (ie to  
avoid having code like: f = Foo.new; f.bar = “hey”; f.whatever =  
“hi”).

Mocha primarily adds methods to Test::Unit::TestCase, whereas lay adds  
the  
lay() method to Class.

Mocha does look pretty nice though. I’ll probably make use of it for  
creating mock objects etc…

–Craig