# Loops and Iterators Difference

**URL:** <https://www.ruby-forum.com/t/loops-and-iterators-difference/152172>\
**Category:** Ruby\
**Created:** [October 30, 2008, 7:30pm UTC](https://www.ruby-forum.com/t/loops-and-iterators-difference/152172 "2008-10-30T19:30:06Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sohdubom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dfb087/32.png) [@sohdubom](https://www.ruby-forum.com/u/sohdubom)\
**Post date:** [October 30, 2008, 7:30pm UTC](https://www.ruby-forum.com/t/loops-and-iterators-difference/152172/1 "2008-10-30T19:30:06Z")

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Hi. The way I understand, both loops and iterators are, ‘loops’, but the  
sutil difference is that a loop is used to just loop several times and  
an iterators loops several times and also access some attribute of the  
element being loop.

I’m actually trying to find a better and clear explanation of the  
difference between loop and iterator.

---

<div class="post-metadata">

**Author:** ![sohdubom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dfb087/32.png) [@sohdubom](https://www.ruby-forum.com/u/sohdubom)\
**Post date:** [October 30, 2008, 9:10pm UTC](https://www.ruby-forum.com/t/loops-and-iterators-difference/152172/2 "2008-10-30T21:10:18Z")

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2008/10/30 Soh D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> Hi. The way I understand, both loops and iterators are, ‘loops’, but the  
> sutil difference is that a loop is used to just loop several times and  
> an iterators loops several times and also access some attribute of the  
> element being loop.
> 
> I’m actually trying to find a better and clear explanation of the  
> difference between loop and iterator.

An iterator is an object that allows us to traverse the  
elements of a data structure. In Ruby we usually use  
“internal” iterators, that means we don’t need to explicitly  
manage an iterator object:

```
my_tree.each_node { |node| node.do_something }

```

Using an external iterator (in combination with a loop!) could look  
like this:

```
iterator = my_tree.each_node_iterator
while iterator.has_next?
  node = iterator.next
  node.do_something
end

```

In both cases, the iterator allows us to traverse the data  
structure without knowledge about its internals. Which frees  
us to change the implementation later without changing  
client code.

A loop simply means repeating a sequence of statements,  
endlessly in the simplest case:

```
loop { do_something }

```

We could use a loop to traverse a data structure,  
say a linked list:

```
item = people
while item
  item.object.do_something
  item = item.next
end

```

But this code breaks when we decide to use e.g. an array  
instead of a list to store people.

Stefan

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<div class="post-metadata">

**Author:** ![sohdubom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dfb087/32.png) [@sohdubom](https://www.ruby-forum.com/u/sohdubom)\
**Post date:** [October 31, 2008, 11:32am UTC](https://www.ruby-forum.com/t/loops-and-iterators-difference/152172/3 "2008-10-31T11:32:32Z")

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Thanks Stefan … very good explanation 🙂