# Re: while vs loop

**URL:** <https://www.ruby-forum.com/t/re-while-vs-loop/160921>\
**Category:** Ruby\
**Created:** [February 20, 2009, 10:58pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921 "2009-02-20T22:58:36Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 20, 2009, 10:58pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/1 "2009-02-20T22:58:36Z")

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Hi,I saw this thread from last week: while vs loop,

I don’t think anybody mentioned the slight performance difference  
between  
the two,  
(or maybe I got the wrong info!!)  
In fact, I had always assumed the ‘loop do’ construct to be better than  
‘while 1 do’, if only to be more elegant or concise for implementing  
infinite loops… but it turns out it seems to be the other way:

##############  
require ‘benchmark’  
Benchmark.bm do |x|  
x.report(‘while1’) do  
n = 0  
while 1 do  
break if n \>= 10000000  
n += 1  
end  
end  
x.report('loop ') do  
n = 0  
loop do  
break if n \>= 10000000  
n += 1  
end  
end  
end

##############  
RESULTS:

```
               user system total real

```

while 1 19.770000 0.230000 20.000000 ( 34.458926)  
loop 25.870000 0.300000 26.170000 ( 42.804569)

###########

I’m running this benchmark on 1.8.6 patchlevel 114 (universal-darwin9.0)

So why is it behaving this way?  
Are every implementations doing the same?

Thanks!

L-P

On Sat, Feb 14, 2009 at 7:16 AM, Nobuyoshi N.  
\<n…[http://groups.google.com/groups/unlock?\_done=/group/ruby-talk-google/browse\_thread/thread/3ee74ef131ec90ba&msg=2f988b0deb69e61d](http://groups.google.com/groups/unlock?_done=/group/ruby-talk-google/browse_thread/thread/3ee74ef131ec90ba&msg=2f988b0deb69e61d)  
@ruby-lang.org\> wrote:

> Hi,

> At Sat, 14 Feb 2009 15:03:03 +0900,  
> Vetrivel V. wrote in [ruby-talk:328175]:
> 
> > what is the Difference between loop and while in ruby ?

> > loop do  
> > end

> loop is a kernel method which takes a block. A block  
> introduces new local variable scope.

> loop do  
> a = 1  
> break  
> end  
> p a #=\> causes NameError

> > while 1  
> > end

> while doesn’t.

> while 1  
> a = 1  
> break  
> end  
> p a #=\> 1

> –  
> Nobu Nakada

furthermore loop do has an implicit rescue clause for a StopIteration  
exception  
(I believe 1.8.7 and 1.9.1 only IIRC)

therefore

loop do  
some\_enumerator.next  
end  
becomes a convenient idiom.

HTH  
Robert

---

<div class="post-metadata">

**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 20, 2009, 11:22pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/2 "2009-02-20T23:22:45Z")

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On Feb 20, 2009, at 13:57 , Louis-Philippe wrote:

> Hi,I saw this thread from last week: while vs loop,
> 
> I don’t think anybody mentioned the slight performance difference  
> between  
> the two,

If you’re going to talk performance differences between while and  
loop, don’t forget for and each:

> ```
> user system total real
> 
> ```
> 
> each 1.370000 0.010000 1.380000 ( 1.380012)  
> for 1.630000 0.000000 1.630000 ( 1.652562)  
> each-var 2.450000 0.010000 2.460000 ( 2.479478)  
> while 5.510000 0.010000 5.520000 ( 5.532909)  
> loop 7.730000 0.020000 7.750000 ( 7.786959)

require ‘benchmark’

max = (ARGV.shift || 1\_000\_000).to\_i

puts “# of iterations = #{max}”  
Benchmark::bm(20) do |x|  
x.report(“each”) do  
(0…max).each do  
end  
end

x.report(“for”) do  
for i in 0…max do  
# do nothing  
end  
end

x.report(“each-var”) do  
(0…max).each do |i|  
end  
end

x.report(“while”) do  
n = 0  
while true do  
break if n \>= max  
n += 1  
end  
end

x.report(“loop”) do  
n = 0  
loop do  
break if n \>= max  
n += 1  
end  
end  
end

---

<div class="post-metadata">

**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 12:03am UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/3 "2009-02-21T00:03:55Z")

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mmm, Interesting to see loop being this high in the list,  
but even if they all loop from 0 to X doesn’t mean they can all  
compared…  
I’m not sure what was the initial question (!!!), but mine is about  
infinite  
loop implementations,  
where list iterators of the .each flavour don’t do.

So _THE_ fastest ruby infinite loop is ‘while 1’?

2009/2/20 Ryan D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

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**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 3:44pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/4 "2009-02-21T15:44:05Z")

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On Fri, Feb 20, 2009 at 6:02 PM, Louis-Philippe  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> mmm, Interesting to see loop being this high in the list,  
> but even if they all loop from 0 to X doesn’t mean they can all  
> compared…  
> I’m not sure what was the initial question (!!!), but mine is about  
> infinite  
> loop implementations,  
> where list iterators of the .each flavour don’t do.
> 
> So _THE_ fastest ruby infinite loop is ‘while 1’?

## Anything purporting to be an infinite loop which runs faster than something which is an infinite loop is, by definition NOT an infinite loop!

Rick DeNatale

Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)  
Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale)  
WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale)  
LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)

---

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**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 9:52am UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/5 "2009-02-21T09:52:06Z")

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On Feb 20, 2009, at 15:02 , Louis-Philippe wrote:

> mmm, Interesting to see loop being this high in the list,  
> but even if they all loop from 0 to X doesn’t mean they can all  
> compared…  
> I’m not sure what was the initial question (!!!), but mine is about  
> infinite  
> loop implementations,  
> where list iterators of the .each flavour don’t do.
> 
> So _THE_ fastest ruby infinite loop is ‘while 1’?

wrong

---

<div class="post-metadata">

**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 4:50pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/6 "2009-02-21T16:50:51Z")

</div>

Rick DeNatale wrote:

> Anything purporting to be an infinite loop which runs faster than something  
> which is an infinite loop is, by definition NOT an infinite loop!

Not sure Georg Cantor would agree with you. One infinite loop might  
only go through a countable (but infinite) number of iterations, i.e.  
aleph null, whereas another might go through an uncountable number of  
iterations.

Suppose one loop iterates over just the rationals, while another  
iterates over the reals. The former iterates fewer times than the  
latter, even though both are infinite.

Still, your point is well taken. 🙂

---

<div class="post-metadata">

**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 5:56pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/7 "2009-02-21T17:56:23Z")

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On Sat, Feb 21, 2009 at 3:42 PM, Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> On Fri, Feb 20, 2009 at 6:02 PM, Louis-Philippe [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> Anything purporting to be an infinite loop which runs faster than something  
> which is an infinite loop is, by definition NOT an infinite loop!  
>   
> This was one of the most famous stories in our department . We were  
> developing a Debugger and my colleague was debugging an infinite loop,  
> which happened to be inside another infinite loop. Of course he did  
> not discover the problem of the outer infinite loop before having  
> fixed the inner one.  
> When our project leader asked him about the progress he had made, he  
> genuinely replied: “It still loops, but much faster”. We happened to  
> pull his leg for quite some time of course :)?  
> Robert

---

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**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 23, 2009, 6:04pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/8 "2009-02-23T18:04:40Z")

</div>

This is indeed very fun and mind boggling!Still, pragmatically, not all  
infinite loops are equal, in the performance of their implementations  
that  
is.  
So taking Ryan’s idea to twist iterators to perform infinite loops, here  
is  
the benchmark again.

For the comparison to be as close as possible between the control  
structures, I use the same inner routine for all, ignoring the fact that  
I  
could derive incrementation from the infinite range iteration, because  
this  
is not the subject of the benchmark.

Ruby Infinite loops Inplementations:  
user system total real  
while1 31.960000 0.150000 32.110000 ( 36.749597)  
loop 42.240000 0.190000 42.430000 ( 45.533708)  
Infinite.each 108.400000 0.970000 109.370000 (117.421059)  
for Infinite 112.070000 1.010000 113.080000 (126.712828)

#############

Benchmark.bm do |x|  
x.report(‘while1’) do  
n = 0  
while 1 do  
break if n \>= 1000000  
n += 1  
end  
end  
x.report(‘loop’) do  
n = 0  
loop do  
break if n \>= 1000000  
n += 1  
end  
end  
x.report(‘Infinite.each’) do  
n = 0  
(0…(1/0.0)).each do  
break if n \>= 1000000  
n += 1  
end  
end  
x.report(‘for Infinite’) do  
n = 0  
for i in (0…(1/0.0)) do  
break if n \>= 1000000  
n += 1  
end  
end  
end

#############

2009/2/21 Robert D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

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**Author:** ![Louis-Philippe](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/db5fbb/32.png) [@Louis-Philippe](https://www.ruby-forum.com/u/Louis-Philippe)\
**Post date:** [February 21, 2009, 5:57pm UTC](https://www.ruby-forum.com/t/re-while-vs-loop/160921/9 "2009-02-21T17:57:34Z")

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On Sat, Feb 21, 2009 at 4:49 PM, Jeff S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Rick DeNatale wrote:
> 
> > Anything purporting to be an infinite loop which runs faster than  
> > something  
> > which is an infinite loop is, by definition NOT an infinite loop!
> 
> Not sure Georg Cantor would agree with you. One infinite loop might only go  
> through a countable (but infinite) number of iterations, i.e. aleph null,  
> whereas another might go through an uncountable number of iterations.  
> Might it? I do not think so! I believe that a Turing complete language  
> can only loop countable times, which of course should be fixed ;).  
> R.