Using hash keys as object name

Ruby
1

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.

2

On Wed, Apr 20, 2011 at 8:07 AM, neubyr [email protected] 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

3

Neubyr N. 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”=>""}

In short, there is no need to create variables with those names. Hashes
associate names(keys) with values, so use a hash. Your
question usually comes up in the form: “Hi, I want to create variables
with the names a1, a2, a3, a4, a5 … a100. How can I do that?” The
answer is: that’s what arrays are for. You just have to settle for the
names being a[0], a[1], a[2] … a[99] instead.

4

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 K.

5

On Wed, Apr 20, 2011 at 11:19 PM, neubyr [email protected] 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

6

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

–
neuby