# Name of a variable, at runtime

**URL:** <https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912>\
**Category:** Ruby\
**Created:** [November 12, 2007, 4:31am UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912 "2007-11-12T04:31:44Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![banry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/898d66/32.png) [@banry](https://www.ruby-forum.com/u/banry)\
**Post date:** [November 12, 2007, 4:31am UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912/1 "2007-11-12T04:31:44Z")

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This seems harder than the usual thing I’ve been tripping on (and  
finding answers in the pickaxe or online).

I have an object: human. It has parts: human.hand human.foot.

How can I say this:  
fred = human.new  
fred.hand = fred.foot = fred. leg = ‘flesh’  
fred.knee = ‘plastic’  
fred.head = ‘steel’  
parts = [hand,foot,leg,knee]  
parts.each do |part|  
puts "part #{part} is made of " + fred.{part}.to\_s  
end # with each part

Am I close?

Thanks,  
–Colin

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**Author:** ![banry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/898d66/32.png) [@banry](https://www.ruby-forum.com/u/banry)\
**Post date:** [November 12, 2007, 5:02am UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912/2 "2007-11-12T05:02:31Z")

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Colin S. wrote:

> This seems harder than the usual thing I’ve been tripping on (and  
> finding answers in the pickaxe or online).
> 
> I have an object: human. It has parts: human.hand human.foot.
> 
> How can I say this:  
> fred = human.new  
> fred.hand = fred.foot = fred. leg = ‘flesh’  
> fred.knee = ‘plastic’  
> fred.head = ‘steel’  
> parts = [hand,foot,leg,knee]  
> parts.each do |part|  
> puts "part #{part} is made of " + fred.{part}.to\_s  
> end # with each part
> 
> Am I close?
> 
> Thanks,  
> –Colin

I think that ‘object.send(method)’ gives you what you want:

class Human  
attr\_accessor :hand, :foot, :leg, :knee, :head  
end

fred = Human.new  
fred.hand = fred.foot = fred. leg = ‘flesh’  
fred.knee = ‘plastic’  
fred.head = ‘steel’  
parts = %w[hand foot leg knee]

parts.each do |part|  
puts "part #{part} is made of " + fred.send(part)  
end

Raul

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<div class="post-metadata">

**Author:** ![banry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/898d66/32.png) [@banry](https://www.ruby-forum.com/u/banry)\
**Post date:** [November 12, 2007, 5:04am UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912/3 "2007-11-12T05:04:31Z")

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On Nov 11, 2007, at 10:30 PM, Colin S. wrote:

> ```
> parts = [hand,foot,leg,knee]
> parts.each do |part|
> puts "part #{part} is made of " + fred.{part}.to_s
> end # with each part
> 
> ```
> 
> Am I close?

Close, yes, but not quite there. Assuming you want to roll your own  
Human class, then you can do something like:

`
class Human
    attr_accessor :hand, :leg, :foot, :head, :knee
end
fred = Human.new
fred.hand = fred.foot = fred.leg = ‘flesh’
fred.knee = ‘plastic’
fred.head = ‘steel’
parts = %w[hand foot leg knee]
parts.each do |part|
puts “part #{part} is made of #{fred.send(part)}”
end
`

OTOH, you might look at the built-in Struct class. It may do  
everything you want.

Regards, Morton

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<div class="post-metadata">

**Author:** ![banry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/898d66/32.png) [@banry](https://www.ruby-forum.com/u/banry)\
**Post date:** [November 12, 2007, 11:35pm UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912/4 "2007-11-12T23:35:59Z")

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Well, technically it will be a Rails object, so I don’t create it,  
ActiveRecord does, but I bet the send(part) thing will work. Thanks.  
This will make a really LOOOOONG table get generated with a few lines  
of code instead.

–Colin

---

<div class="post-metadata">

**Author:** ![banry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/898d66/32.png) [@banry](https://www.ruby-forum.com/u/banry)\
**Post date:** [November 13, 2007, 6:22am UTC](https://www.ruby-forum.com/t/name-of-a-variable-at-runtime/119912/5 "2007-11-13T06:22:48Z")

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Colin S. wrote:

> Well, technically it will be a Rails object, so I don’t create it,  
> ActiveRecord does, but I bet the send(part) thing will work. Thanks.  
> This will make a really LOOOOONG table get generated with a few lines  
> of code instead.
> 
> –Colin

In case you wanted an explanation of how things work, take a look at  
this example:

class Human  
def knee=(str)  
@knee = str  
end

def knee  
return @knee  
end

end

fred = Human.new  
fred.knee = ‘plastic’  
puts fred.knee  
—\>plastic

When you write:

fred.knee = ‘plastic’

you are actually calling a method–the method named ‘knee=’. In Ruby,  
method names can have characters like ‘=’ and ‘?’ in them. When the  
method ‘knee=’ is called, the statement in the body of the method is  
executed, and that statement assigns a value to the member variable  
@knee.

Likewise, when you write:

puts fred.knee

that calls the method named ‘knee’, and the knee method is defined to  
return the value of the member variable @knee.

Therefore, the problem you were faced with becomes: how do you call a  
method if you have the name of the method as a string. That’s where  
Object#send comes in–it allows you to do just that.

Although it wouldn’t make much sense, you could actually define the  
knee= method like this:

class Human  
def knee=(str)  
@head = str  
end

def head  
return @head  
end

end

fred = Human.new  
fred.knee = ‘steel’  
puts fred.head  
—\>steel