From: Mike Stok <mike@...>
Date: 2013-05-24T20:49:56+09:00
Subject: Re: Learning and stuck `OpenStruct` standard library of Ruby


On 2013-05-24, at 6:44 AM, Love U Ruby <lists@ruby-forum.com> wrote:

> Hi,
> 
> I was learning Ruby's standard library `OpenStruct`. And doing so,out of
> curiosity wrote the below code:
> 
> require 'ostruct'
> 
> person = OpenStruct.new
> person.name    = "John Smith"
> person.age     = 70
> person.pension = 300
> 
> p person.instance_variables #=> [:@table, :@modifiable]
> 
> Now my question is - Where the above 2 instance variables have been
> defined? What are their uses.
> 
> On the same not I also not able to understand the method `#modifiable`.
> (http://www.ruby-doc.org/stdlib-2.0/libdoc/ostruct/rdoc/OpenStruct.html#method-i-modifiable).
> 
> Can any one help me to understand the same?

You might be able to help yourself by using a tool like pry http://pryrepl.org to look at the variables and source.  For example

ratdog:~ mike$ pry
[1] pry(main)> require 'ostruct'
=> false
[2] pry(main)>
[3] pry(main)> person = OpenStruct.new
=> #<OpenStruct>
[4] pry(main)> person.name    = "John Smith"
=> "John Smith"
[5] pry(main)> person.age     = 70
=> 70
[6] pry(main)> person.pension = 300
=> 300
[7] pry(main)> person
=> #<OpenStruct name="John Smith", age=70, pension=300>
[8] pry(main)> cd person
[9] pry(#<OpenStruct>):1> $ to_s

From: /Users/mike/.rbenv/versions/2.0.0-p0/lib/ruby/2.0.0/ostruct.rb @ line 232:
Owner: OpenStruct
Visibility: public
Number of lines: 21

def inspect
  str = "#<#{self.class}"

  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    return str << ' ...>'
  end

  ids << object_id
  begin
    first = true
    for k,v in @table
      str << "," unless first
      first = false
      str << " #{k}=#{v.inspect}"
    end
    return str << '>'
  ensure
    ids.pop
  end
end

I have found pry and its add-ons to be very useful for exploring bits of ruby code.

Mike

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.