From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-01-10T05:08:43+09:00
Subject: Re: Class instance variable question

On Mon, Jan 9, 2012 at 7:26 PM, Matt Mencel <MR-Mencel@wiu.edu> wrote:
> Hi,
>
> I have this class (below) that takes a deeply nested hash and returns back a new hash without all the nesting.  The problem I'm having is that it seems to be that @all_values is not empty if I call it a second time from my program.  First time is fine, but the next time I use get_all_values_nested, @all_values still has the results in it from the first time it was used.
>
> Any thoughts on what I'm doing wrong?  I just want @path and @all_values to be empty each time I use the get_all_values_nested function.
>
> Thanks,
> Matt
>
>
>
>
> class Tools
>
>  @path = []
>  @all_values = {}
>
>  def self.get_all_values_nested(nested_hash={})
>    puts "ALL VALS: #{@all_values}"
>    nested_hash.each_pair do |k,v|
>      @path << k
>      case v
>        when Array, DateTime, FalseClass, Fixnum, NilClass, String, TrueClass then
>          @all_values.merge!({"#{@path.join(".")}" => "#{v}"})
>          @path.pop
>        when Hash then get_all_values_nested(v)
>        else raise ArgumentError, "Unhandled type #{v.class}"
>      end
>    end
>    @path.pop
>
>    return @all_values
>  end
>
> end

Instance variables keep their value after the method execution, that's
why you are seeing that problem.
Instead of using an instance variable you could just use the return
value of the recursive call to merge it to a local variable that you
then return. This way you won't need instance variables at all:

require 'date'

class Tools
  def self.get_all_values_nested(nested_hash={}, path=[])
    all_values = {}
    nested_hash.each_pair do |k,v|
      path << k
      case v
        when Array, DateTime, FalseClass, Fixnum, NilClass, String,
TrueClass then
          all_values.merge!({"#{path.join(".")}" => "#{v}"})
        when Hash then
          all_values.merge!(get_all_values_nested(v, path))
        else
          raise ArgumentError, "Unhandled type #{v.class}"
      end
      path.pop
     end
     return all_values
  end
end

p Tools.get_all_values_nested({"a" => 1, "b" => {:first => "1"}})
p Tools.get_all_values_nested({"a" => {"first_level" => 42, "nested"
=> {"key" => "value"}}, "b" => {:first => "1"}})

$ ruby nested_hash.rb
{"a"=>"1", "b.first"=>"1"}
{"a.first_level"=>"42", "a.nested.key"=>"value", "b.first"=>"1"}

Does this help?

Jesus.