Globals outside of OO scripting

ruby-talk
1

When writing methods as functions (I know they're methods pretending to be functions) do you still need to use globals... like this:

$global_var
def some_other_function
    ...
    $global_var
end

Or, is it OK to use them like this:

global_var
def some_other_function
    ...
    global_var
end

2

rtilley wrote:

When writing methods as functions (I know they're methods pretending to
be functions) do you still need to use globals... like this:

$global_var
def some_other_function
    ...
    $global_var
end

Or, is it OK to use them like this:

global_var
def some_other_function
    ...
    global_var
end

No, you still need to use either global or instance variable syntax, since
it is, as you correctly state, still a class.

def some_other_function
    @n = 1
    $m = 2
end
def some_other_function2
    puts @n
    puts $m
end

some_other_function
some_other_function2

3

When writing methods as functions (I know they're methods pretending to be functions) do you still need to use globals... like this:

$global_var
def some_other_function
   ...
   $global_var
end

Or, is it OK to use them like this:

No

global_var
def some_other_function
   ...
   global_var
end

global_var isn't global here.

···

On Mar 8, 2006, at 4:18 PM, rtilley wrote:

4

but why? at the very least do

   class Main
     def initialize
       @foo = 42
     end
     def run
       p @foo
     end
   end

   Main::new unless $0 == __FILE__

save the namespaces! :wink:

-a

···

On Thu, 9 Mar 2006, rtilley wrote:

When writing methods as functions (I know they're methods pretending to be functions) do you still need to use globals... like this:

$global_var
def some_other_function
  ...
  $global_var
end

Or, is it OK to use them like this:

global_var
def some_other_function
  ...
  global_var
end

--
knowledge is important, but the much more important is the use toward which it
is put. this depends on the heart and mine the one who uses it.
- h.h. the 14th dali lama

5

Bernhard 'elven' Stoeckner wrote:

rtilley wrote:

When writing methods as functions (I know they're methods pretending to
be functions) do you still need to use globals... like this:

$global_var
def some_other_function
   ...
   $global_var
end

Or, is it OK to use them like this:

global_var
def some_other_function
   ...
   global_var
end

No, you still need to use either global or instance variable syntax, since
it is, as you correctly state, still a class.

OK, but the script works wheter I use $ for globals and @ for instance variables or not. With small scripts, why does it matter?

6

Whether you use globals or top-level instance variables for a small script is pretty much
irrelevant but what happens when your small script gets bigger or you want to reuse it in a larger
project? Or you want to merge two small scripts to solve a slightly bigger problem?
You'll have to wrap you little script in a class anyway and in that context the globals/instance
variable solution isn't going to work.

Much easier just to wrap it all in a trivial class to start with as Ara suggested.
The very fact that you are using globals to provide a common state across functions
or function calls cries out for a class/object solution to package that state.

If it was drudgery to create a class then maybe it would be an issue
but it is soooo easy in Ruby, so why fight it?

Gary Wright

···

On Mar 8, 2006, at 4:53 PM, rtilley wrote:

OK, but the script works wheter I use $ for globals and @ for instance variables or not. With small scripts, why does it matter?

7

Bernhard 'elven' Stoeckner wrote:
> rtilley wrote:
>>Or, is it OK to use them like this:
>>
>>global_var
>>def some_other_function
>> ...
>> global_var
>>end
>
> No, you still need to use either global or instance variable syntax, since
> it is, as you correctly state, still a class.

OK, but the script works wheter I use $ for globals and @ for instance
variables or not. With small scripts, why does it matter?

I'm curious what your script is then. Because the variable will not be
shared -- the global_var inside some_other_function is different than
the global_var outside the function. Try this:

  $ irb

  >> global_var = 2
  => 2

  >> def test1
  >> global_var
  >> end
  => nil

  >> def test2
  >> global_var = 5
  >> end
  => nil

  >> global_var
  => 2

  >> test1
  => nil

  >> test2
  => 5

  >> global_var
  => 2

Jacob Fugal

···

On 3/8/06, rtilley <rtilley@vt.edu> wrote:

8

  $ irb

  >> global_var = 2
  => 2

  >> def test1
  >> global_var
  >> end
  => nil

<snip>

  >> test1
  => nil

D'oh, I should have actually tested that *before* posting. This
actually raises a NameError exception, since the global_var referred
to in test1 doesn't even exist!

Jacob Fugal

···

On 3/8/06, Jacob Fugal <lukfugl@gmail.com> wrote:

9

gwtmp01@mac.com wrote:

Much easier just to wrap it all in a trivial class to start with as Ara suggested.

OK, say I have this:

class Thing

   @@class_var = "filename"

   def method
     @method_var = "a_string"
     ...
   end

end

How can I get to these variables outside of the class.

10

You can't, that's kind of the point. You can write accessors (or setters and getters, whatever terminology you prefer)

e.g.

class Thing
    def method_var=(value)
          @method_var = value
     end
    def method_var()
          @method_var
    end
end

To save typing you can use
attr_accessor

class Thing
    attr_accessor :method_var
end

t = Thing.new

t.method_var = 3

t.method_var
#=> 3

···

On Mar 8, 2006, at 7:58 PM, rtilley wrote:

gwtmp01@mac.com wrote:

Much easier just to wrap it all in a trivial class to start with as Ara suggested.

OK, say I have this:

class Thing

  @@class_var = "filename"

  def method
    @method_var = "a_string"
    ...
  end

end

How can I get to these variables outside of the class.

11

class Thing
   def Thing.get_cvar
      return @@class_var
   end
   def get_mvar
       return @method_var
   end
end

# Elsewhere in your code:
puts Thing.get_cvar
puts Thing.new.get_mvar
- - - -
Note that in the case of method-variables, you can use
the even easier shorthand of:

    attr_reader :method_var

and then you'd get the value via:

puts Thing.new.method_var

where '@method_var' would be the name of the instance-
variable whose value will be returned by the method named
'method_var'.

Also note that you may confuse yourself by thinking of
@-variables as "method variables". They are instance
variables. The same value is seen by all methods for
any given instance of the class.

···

On 3/8/06, rtilley <rtilley@vt.edu> wrote:

OK, say I have this:

  class Thing

     @@class_var = "filename"

     def method
       @method_var = "a_string"
       ...
     end

  end

How can I get to these variables outside of the class.

--
Garance Alistair Drosehn = drosihn@gmail.com
Senior Systems Programmer or gad@FreeBSD.org
Rensselaer Polytechnic Institute; Troy, NY; USA

12

Thanks for the examples and info guys!

I'm still trying to get my head around the whole OO concept... as you can probably tell :slight_smile: I don't know if this is proper or not, but I ended up making a constant in the class. Inside, the methods could access it by name. And outside, I could access it like this Class_Name::Constant

Is that good or bad?

13

Depends. Why are you accessing it outside the class? If its to change its value, than thats probably not a good idea and that functionality should be put into a method. Of course if its really a constant, well then its ok.

···

On Mar 8, 2006, at 8:48 PM, rtilley wrote:

Thanks for the examples and info guys!

I'm still trying to get my head around the whole OO concept... as you can probably tell :slight_smile: I don't know if this is proper or not, but I ended up making a constant in the class. Inside, the methods could access it by name. And outside, I could access it like this Class_Name::Constant

Is that good or bad?

14

Logan Capaldo wrote:

Depends. Why are you accessing it outside the class? If its to change its value, than thats probably not a good idea and that functionality should be put into a method. Of course if its really a constant, well then its ok.

It's a filepath (c:\name_of_file) I only wanted to define the path once and be able to read it inside and outside the class. I am not changing it.

15

Hmm, this makes me wonder if maybe your class should look like this:

class NeedsAPath
    def initialize(path, ...)
          @path = path
           ...
   end
   ...
end

...

obj = NeedsAPath.new('c:\name_of_file')

···

On Mar 9, 2006, at 3:38 AM, rtilley wrote:

Logan Capaldo wrote:

Depends. Why are you accessing it outside the class? If its to change its value, than thats probably not a good idea and that functionality should be put into a method. Of course if its really a constant, well then its ok.

It's a filepath (c:\name_of_file) I only wanted to define the path once and be able to read it inside and outside the class. I am not changing it.