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up vote 1 down vote favorite

I realize this may be against ruby principle and may seem a bit silly, but I am curious to whether it possible to modify the index variable during iteration of a loop in ruby.

This practice is possible in Java/C with the for loop in this contrived example:

for (int k = 0; k < 10; k++)
{
   if (k == 5)
      k = 8;
}

As well, I am aware that it is possible to access an index variable with Enumerable#each_with_index, but I am interested with the ability to alter the variable in this instance rather than access it.

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5  
Why do you want to do this? –  squiguy Jun 7 '13 at 2:31
    
As fotanus said -- it is possible to mimic this code in ruby, but I can't imagine any real problem that would be solved this way. –  samuil Jun 7 '13 at 8:07
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3 Answers

up vote 2 down vote

actually the for semantic is the following:

for(executed_once_before_all; test; execute_every_loop) { /* code */ }

and so, in ruby:

executed_once_before_all
while test do
  execute_every_loop
  # code
end

so your exemple is like this:

k = 0
while k < 10 do
  k += 1
  k = 8 if (k == 5)
end
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up vote 0 down vote

Changing for loop counter in Ruby does not change the number of iterations.

You can change the counter variable, but that will affect the current iteration only:

> for k in 0...10
>   k = 8 if k == 5
>   puts k
> end
0
1
2
3
4
8  # Note this!
6
7
8
9

The best way to achieve the desired behaviour is to use while loop as @fotanus suggested.

Of course, you can do that with for loop using next statements, but that's much more ugly:

for k in 0...10
  next if k > 5 && k <= 8
  ... do stuff ...
  next if k == 5
  ... do stuff ...
end
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up vote -1 down vote

You could do that, but Ruby programmers generally don't use the for loop (although it's available). You could also do something like this:

[0,1,2,3,4,5,8,9,10].each do |index|
  # your code here
end
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