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using hash keys as object name

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  using hash keys as object name neubyr <neubyr@gmail.com> - 2011-04-20 01:07 -0500
    Re: using hash keys as object name Robert Klemme <shortcutter@googlemail.com> - 2011-04-20 02:36 -0500
      Re: using hash keys as object name neubyr <neubyr@gmail.com> - 2011-04-20 16:19 -0500
        Re: using hash keys as object name Robert Klemme <shortcutter@googlemail.com> - 2011-04-21 02:23 -0500
          Re: using hash keys as object name neubyr <neubyr@gmail.com> - 2011-04-22 20:40 -0500
    Re: using hash keys as object name 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-20 13:15 -0500

#3210 — using hash keys as object name

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.

thanks,
neuby.

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#3217

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/

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#3269

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/
>
>

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#3296

On Wed, Apr 20, 2011 at 11:19 PM, neubyr <neubyr@gmail.com> wrote:
> 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.

There is no need to create local variables for these File objects - in
fact, it won't work.  You rather want to create a second Hash.

FileData = Struct.new :io, :attributes

user_input = { ... } # from YAML

files = {}

user_input.each do |k,v|
  files[k] = FileData.new File.open(k), v # whatever else
end

# use files
..

# close files
files.each do |k,v|
  v.io.close
end

Note, I deliberately left out error handling in order to keep the code simple.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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#3393

Thanks a lot for explaining the basics.. Changed the implementation.

--
neuby

On 4/21/11, Robert Klemme <shortcutter@googlemail.com> wrote:
> On Wed, Apr 20, 2011 at 11:19 PM, neubyr <neubyr@gmail.com> wrote:
>> 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.
>
> There is no need to create local variables for these File objects - in
> fact, it won't work.  You rather want to create a second Hash.
>
> FileData = Struct.new :io, :attributes
>
> user_input = { ... } # from YAML
>
> files = {}
>
> user_input.each do |k,v|
>   files[k] = FileData.new File.open(k), v # whatever else
> end
>
> # use files
> ...
>
> # close files
> files.each do |k,v|
>   v.io.close
> end
>
> Note, I deliberately left out error handling in order to keep the code
> simple.
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestpractices.com/
>
>

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#3264

Neubyr Neubyr wrote in post #993923:
> 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.
>
> thanks,
> neuby.

fruits = {"apple" => ["green", "red"], "melons" => ["water", "musk"] }

h = {}

fruits.keys.each do |key|
  h[key] = ""
end

p h

--output:--
{"apple"=>"", "melons"=>""}


h['apple'] = 10
p h

--output:--
{"apple"=>10, "melons"=>""}

--output:--

-- 
Posted via http://www.ruby-forum.com/.

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