Get the name of variable with which a method was approached from this class in Ruby

Question

I want to get the name of variable with which class was approached IN the method of the class. Like that:

class Object
  def my_val
    "#{???} = '#{self.to_s}'"
  end
end

a1 = "val1"
a1.my_val # = a1 = 'val1'
a2 = "val2"
a2.my_val # = a2 = 'val2'

Can I do it?

@ArupRakshit, sorry, I do not know how to explain it. I think the example is clear. — Tolsi, Oct 18 '13 at 15:40
you used only `def` but it should be `def..end` block. http://ruby-doc.org/docs/keywords/1.9/Object.html#method-i-def — Arup Rakshit, Oct 18 '13 at 15:41
@ArupRakshit, oh, i'm just beginner with ruby, this was the style of scala :) fixed — Tolsi, Oct 18 '13 at 15:43
@ArupRakshit I want to get the name of the variable of object, to which the method has been called, inside the method of the object >_ — Tolsi, Oct 18 '13 at 15:45
@Stefan why not? :) i want to insert the variables into url with the values by transforming them to "name=value" string and i want to get syntax like address.to_url_param — Tolsi, Oct 18 '13 at 16:56

score 3 · Accepted Answer · answered Oct 18 '13 at 15:55

An object has no idea what variable it may or may not be stored in, and in many cases this is a completely meaningless concept.

What would you expect to happen here?

ref = Object.new
another_ref = ref
@ref = another_ref
hash = { key: @ref }
array = [ hash[:key] ]
array[0].my_val
# => ...?

There are so many ways to reference an object. Knowing which name is being used is irrelevant.

In general terms, variables are just references that are given an arbitrary name that shouldn't matter to the object in question.

What you can do is provide context:

my_var = "test"
my_var.my_val(:my_var)
# => my_var="test"

Implemented as:

def my_var(name)
  "#{name}=#{self.inspect}"
end

You can also roll this up a little and be clever about it:

def dump_var(name)
  "%s=%s" % [ name, instance_variable_get(:"@#{name}").inspect ]
end

Then:

@foo = "test"
dump_var(:foo)
# => foo="test"

I knew that Ruby is good of meta-programming, I thought that this could be real. I like your dump_var method, thanks! — Tolsi, Oct 18 '13 at 16:52
Ruby gives you a lot of reflection capabilities, but some things are not easily exposed. Back-tracing to all the references to an object is one of those things that's theoretically possible, but also not easy. — tadman, Oct 18 '13 at 19:16

score 0 · Answer 2 · edited Oct 18 '13 at 16:12

0

I think the short answer is "NO, you can't :/".

For Ruby (and most languages) the variable name has no meaning. The only one who can give you a hint about variable names is the compiler, and it is in a whole other abstraction level than inside Ruby.

edited Oct 18 '13 at 16:12

the Tin Man

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answered Oct 18 '13 at 15:53

ichigolas

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Get the name of variable with which a method was approached from this class in Ruby

2 Answers2