# Using strings to drill down into objects

**URL:** <https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921>\
**Category:** Ruby\
**Created:** [October 11, 2007, 7:32am UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921 "2007-10-11T07:32:26Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Ross\_X\_Dawson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/779978/32.png) [@Ross\_X\_Dawson](https://www.ruby-forum.com/u/Ross_X_Dawson)\
**Post date:** [October 11, 2007, 7:32am UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921/1 "2007-10-11T07:32:26Z")

</div>

Folks,  
I’m writing a reporting application where I’m passing in an array  
of  
method calls to populate a table

e.g.

```
# lambda function to drill down object hierarchy
drill_down = lambda do |obj, method_name|
                      o ||= obj
                      method_name.split('.').each {|m| o = o.send(m) 

```

if  
o.respond\_to?(m)}  
o  
end

methods = [‘lookup1.code’, ‘lookup1.name’]

report\_value = drill\_down.call(my\_object\_with\_lookups, methods)

I’m sure there is a better “Ruby” way of doing this. Can someone offer  
some advice?

Ross D.  
Developer  
Data Management & Reporting  
Link Administration Services

Tel Direct: (03) 9633 8165  
Tel Office: (03) 9633 8000

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---

<div class="post-metadata">

**Author:** ![Ross\_X\_Dawson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/779978/32.png) [@Ross\_X\_Dawson](https://www.ruby-forum.com/u/Ross_X_Dawson)\
**Post date:** [October 11, 2007, 2:32pm UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921/2 "2007-10-11T14:32:53Z")

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Ross X Dawson wrote:

> report\_value = drill\_down.call(my\_object\_with\_lookups, methods)  
> I’m not sure what your intent is, but I guess this code won’t work.

First, unless you define it before creating the lambda, “o” won’t exist  
in its binding, so you can’t call o ||= obj. Second, you pass an array  
of method names to your lambda as a second parameter, on which #split  
isn’t defined.

You could state instead:

method\_name.each{|name| name.split{|part| … } }

but then, “part” would take the value “lookup1”, “code”, “lookup1”  
again, and “name” in that order. I highly doubt you want this.

However, AFAIK you’re right that o.send(m, \*args) is the way to call an  
arbitrary named method on an object.

mortee

---

<div class="post-metadata">

**Author:** ![Ross\_X\_Dawson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/779978/32.png) [@Ross\_X\_Dawson](https://www.ruby-forum.com/u/Ross_X_Dawson)\
**Post date:** [October 11, 2007, 2:43pm UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921/3 "2007-10-11T14:43:28Z")

</div>

mortee wrote:

> Ross X Dawson wrote:
> 
> > ```
> > # lambda function to drill down object hierarchy
> > drill_down = lambda do |obj, method_name|
> > o ||= obj
> > method_name.split('.').each {|m| o = o.send(m) if
> > 
> > ```
> > 
> > o.respond\_to?(m)}  
> > o  
> > end
> 
> method\_name.each{|name| name.split{|part| … } }

Sorry, that should read

method\_name.each{|name| name.split(’.’).each{|part| … } }

---

<div class="post-metadata">

**Author:** ![Ross\_X\_Dawson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/779978/32.png) [@Ross\_X\_Dawson](https://www.ruby-forum.com/u/Ross_X_Dawson)\
**Post date:** [October 11, 2007, 6:05pm UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921/4 "2007-10-11T18:05:33Z")

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On Oct 11, 8:32 am, mortee [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > report\_value = drill\_down.call(my\_object\_with\_lookups, methods)
> 
> I’m not sure what your intent is, but I guess this code won’t work.
> 
> First, unless you define it before creating the lambda, “o” won’t exist  
> in its binding, so you can’t call o ||= obj.

Are you sure about that?

brian@imagine:~$ irb  
irb(main):001:0\> x ||= 7  
=\> 7  
irb(main):002:0\> x  
=\> 7

---

<div class="post-metadata">

**Author:** ![Ross\_X\_Dawson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/779978/32.png) [@Ross\_X\_Dawson](https://www.ruby-forum.com/u/Ross_X_Dawson)\
**Post date:** [October 11, 2007, 7:02pm UTC](https://www.ruby-forum.com/t/using-strings-to-drill-down-into-objects/116921/5 "2007-10-11T19:02:33Z")

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Brian A. wrote:

> Are you sure about that?
> 
> brian@imagine:~$ irb  
> irb(main):001:0\> x ||= 7  
> =\> 7  
> irb(main):002:0\> x  
> =\> 7

Sorry, you’re right. I’ve never tried this actually on an undefined  
local variable - and I guessed it would first try to evaluate x, which  
would raise an exception. Thanks for pointing that out, I’m happy to  
have learnt it (:

mortee