# Bug or feature?

**URL:** <https://www.ruby-forum.com/t/bug-or-feature/137794>\
**Category:** Ruby\
**Created:** [May 16, 2008, 12:42pm UTC](https://www.ruby-forum.com/t/bug-or-feature/137794 "2008-05-16T12:42:38Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![varezhka](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/53a042/32.png) [@varezhka](https://www.ruby-forum.com/u/varezhka)\
**Post date:** [May 16, 2008, 12:42pm UTC](https://www.ruby-forum.com/t/bug-or-feature/137794/1 "2008-05-16T12:42:38Z")

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Can anybody explain to me what does it mean?

code -\>  
a1 = Array.new(1000000)  
a2 = Array.new(1000000)  
t = Time.now  
1000000.times { |i| a1[i] = i; a2[i] = i }  
print "1. Elapsed time: “, Time.now - t, " seconds\n”  
t = Time.now  
1000000.times { |i| a1[i], a2[i] = i, i }  
print "2. Elapsed time: “, Time.now - t, " seconds\n”

results -\>  
ruby 1.8.6

1. Elapsed time: 0.882 seconds
2. Elapsed time: 11.436 seconds (!!!)  
jruby 1.1.1
3. Elapsed time: 1.669 seconds
4. Elapsed time: 2.249 seconds

---

<div class="post-metadata">

**Author:** ![varezhka](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/53a042/32.png) [@varezhka](https://www.ruby-forum.com/u/varezhka)\
**Post date:** [May 16, 2008, 1:12pm UTC](https://www.ruby-forum.com/t/bug-or-feature/137794/2 "2008-05-16T13:12:11Z")

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2008/5/16 Igor G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> print "2. Elapsed time: “, Time.now - t, " seconds\n”
> 
> results →   
> ruby 1.8.6
> 
> 1. Elapsed time: 0.882 seconds
> 2. Elapsed time: 11.436 seconds (!!!)  
> jruby 1.1.1
> 3. Elapsed time: 1.669 seconds
> 4. Elapsed time: 2.249 seconds

I guess it’s because of the intermediate arrays that are created for  
the second assignment.

Btw, here’s an even faster way:

13:10:16 JBoss$ /c/Temp/ass.rb  
Rehearsal --------------------------------------------------------  
a1[i] = i; a2[i] = i 1.188000 0.000000 1.188000 ( 1.185000)  
a1[i], a2[i] = i, i 14.562000 0.000000 14.562000 ( 14.589000)  
a1[i] = a2[i] = i 1.141000 0.000000 1.141000 ( 1.146000)  
---------------------------------------------- total: 16.891000sec

```
                       user system total real

```

a1[i] = i; a2[i] = i 1.156000 0.000000 1.156000 ( 1.150000)  
a1[i], a2[i] = i, i 14.750000 0.000000 14.750000 ( 14.771000)  
a1[i] = a2[i] = i 1.171000 0.000000 1.171000 ( 1.173000)  
13:10:59 JBoss$ cat /c/Temp/ass.rb  
#!/bin/env ruby

require ‘benchmark’

a1 = Array.new(1000000)  
a2 = a1.dup

Benchmark.bmbm 20 do |x|

x.report “a1[i] = i; a2[i] = i” do  
a1.size.times { |i| a1[i] = i; a2[i] = i }  
end

x.report “a1[i], a2[i] = i, i” do  
a1.size.times { |i| a1[i], a2[i] = i, i }  
end

x.report “a1[i] = a2[i] = i” do  
a1.size.times { |i| a1[i] = a2[i] = i }  
end

end

Kind regards

robert

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<div class="post-metadata">

**Author:** ![varezhka](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/53a042/32.png) [@varezhka](https://www.ruby-forum.com/u/varezhka)\
**Post date:** [May 19, 2008, 9:01am UTC](https://www.ruby-forum.com/t/bug-or-feature/137794/3 "2008-05-19T09:01:21Z")

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Robert K. wrote:

> I guess it’s because of the intermediate arrays that are created for  
> the second assignment.

There isn’t such a problem in 1.9.0.