From: Brian Candler <b.candler@...>
Date: 2011-04-05T21:41:56+09:00
Subject: Re: Autoconvert object from one class1 to other class2 in class1 def

Luk Mus wrote in post #990967:
> But i can get object_id:
>
> class String
>   def get_id
>     puts self.__id__
>     puts self.object_id
>   end
> end

Sure, the object_id is basically the object reference. It's a property 
of the object itself, not of any variable which contains a reference to 
that object.

In ruby, variables are not objects.

> Is it realy to get name by ID?

That question doesn't parse.

If you're asking "Is it really impossible to get the name of the 
variable which holds a particular object_id", then I already said yes, 
and explained why. Consider these cases:

"string".get_my_name # what should it return??

a = "some string"
@b = a
$c = a
a.get_my_name        # what should it return??

h = {:foo => "another string"}
h[:foo].get_my_name  # what should it return??

In any case, with closures, the same local variable can exist multiple 
times with different values. e.g.

def make_adder(n)
  lambda { |x| x+n }
end

a1 = make_adder(1)
a2 = make_adder(100)
puts a1.call(1)  # 2
puts a2.call(1)  # 101

The local variable 'n' has two different values in the two closures.

If you really want to update a local variable remotely, then you can 
look at the 'Binding' class - but I think you really don't. You have to 
pass the binding explicitly, and then use 'eval' to access a local 
variable within that binding.

# DON'T DO THIS!
def increment(var, b)
  eval "#{var} += 1", b
end

a = 10
increment("a", binding)
puts a  # 11

Local variables are not supposed to be abused this way. It's more 
reasonable to do this with instance variables (which means you should be 
thinking about encapsulating long-lived state in objects, not in local 
variables).

def increment(var)
  instance_variable_set(var, instance_variable_get(var) + 1)
end

@a = 20
increment(:@a)
puts @a   # 21

But in most sane applications, you'd use accessor methods on the object 
being passed, not mess around with instance variables directly.

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