How global are global variables in ruby?

Question

Here's a ruby script:

discarded_rows=-1

def foobar(line)

    if line.match('records discarded: *(\d+)') then
       discarded_rows=$1;
       puts('yepp, I have found: ' + discarded_rows);
    end;

end


foobar('records successful:    99    ');
foobar('records discarded:      2    ');
foobar('records unknown:        8    ');

if discarded_rows != 2 then
   puts("discarded_rows: #{discarded_rows}");
end

And here's what I believe it does: it declares a (global) variable with the name discarded_rows. It then declares a function foobar that checks if the passed argument line matches "records discarded *\d". If it does, it assignes the number of discarded records to the (what I think is a global) variable discarded_rows. If it matches, it also prints "yepp...." just to make sure that the match works.

The function is called, with one string that should match.

If discarded_rows is not equal to 2, it prints the according value.

And here's the script's output:

yepp, I have found: 2
discarded_rows: -1

So, clearly, the match worked, and obviously, discarded_rows is not truly global. Is this correct or do I overlook something?

Zabba · Accepted Answer · 2010-12-29 16:04:00Z

8

discarded_rows is not a global variable. $discarded_rows would be a global variable.

answered Dec 29, 2010 at 16:04

Zabba

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Comments

Logan Capaldo · Accepted Answer · 2010-12-29 16:16:57Z

Zabba is absolutely correct. To elaborate a little bit however, discarded_rows is a local variable. Code at the top level is treated roughly as though the whole file was being executed as a method. Defining a new method actually happens much more so at runtime than in most languages, to the point where you can write something like

s = gets
if s =~ /(\d+)/
   i = $1.to_i
   if i < 5
     def less_than_five
       true
     end
   else
     def less_than_five
       false
     end
    end
 else
   def less_than_five
     raise "not a number"
   end
end

p less_than_five

The body of an def end block introduces a new lexical scope that does not close over the enclosing lexical scope (locals in the surrounding code are not available to the body of the method).

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