From: neubyr <neubyr@...>
Date: 2011-04-21T06:19:14+09:00
Subject: Re: using hash keys as object name

Thanks for the help Robert. Following is a scenario I am trying to implement:
I want to create File objects based on a hash. The 'fruits' hash will
be created based on user input (yaml file), so I don't know how long
the hash will be beforehand. For each key in this hash I would like to
instantiate a File object with object/var name same as hash key. In
future I may have a subclass of File class say UserFile class. The
UserFile objects will be instantiated in a similar manner as File
object, in addition they will get hash values passed on as variables.

--
neubyr.


On Wed, Apr 20, 2011 at 2:36 AM, Robert Klemme
<shortcutter@googlemail.com> wrote:
> On Wed, Apr 20, 2011 at 8:07 AM, neubyr <neubyr@gmail.com> wrote:
>> How do I assign hash's key as an object name?  For example I have a hash as:
>>
>>  fruits = {"apple" => ["green", "red"], "melons" => ["water", "musk"] }
>>
>> I would like to create a File or String objects by reading above hash,
>> something like
>>
>>  fruits.keys.each {|k| "#{k}" = String.new}
>>
>> Any hints or suggestions on how to do this will be really helpful.
>
> There is usually no point in dynamically generating local variable
> names - which is what you are trying to attempt.  The reason is that
> your code needs to use them before they are known - otherwise it
> cannot see them.  Example:
>
> 09:35:55 ~$ ruby19 b.rb
> name is foo
> attempt 1
> [:name, :e, :b, :foo]
> 123
> attempt 2
> [:name, :e, :b, :foo]
> 123
> attempt 3
> [:name, :e, :b, :foo]
> 123
> 09:35:57 ~$ cat -n b.rb
>     1
>     2  name='foo'
>     3  puts "name is #{name}"
>     4
>     5  puts "attempt 1"
>     6
>     7
>     8  begin
>     9    eval "#{name}=123"
>    10    p local_variables
>    11    eval "puts #{name}"
>    12  rescue Exception => e
>    13    puts e
>    14  end
>    15
>    16  puts "attempt 2"
>    17
>    18  b = binding
>    19  eval "#{name}=123", b
>    20  p local_variables
>    21  eval "puts #{name}", b
>    22
>    23  puts "attempt 3"
>    24
>    25  foo=nil
>    26  eval "#{name}=123"
>    27  p local_variables
>    28  eval "puts #{name}"
> 09:36:05 ~$
>
> Note there are some special cases where it can make sense.  These
> typically involve meta programming (e.g. ERB does it).
>
> What are you trying to accomplish?
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestpractices.com/
>
>