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From: Diogo Almeida on 13 Jul 2010 08:09
Hello,

The Liquid templating engine has the following tests passing till ruby
1.9.2 rc1:

assert_template_result "4.66666666666667", "{{ 14 | divided_by:'3.0' }}"
#equals to 14/3.0 in irb
assert_template_result "6.3", "{{ '2.1' | times:3 }}" #equals to 2.1*3
in irb

However, as far as I could understand, the float precision has been
changed with RC1 and the first assertion now returns 15 decimal digits
instead of 14:
ruby-1.9.2-rc1 > 14/3.0
=> 4.666666666666667

And the second returns the same 15 decimal digits instead of 1:
ruby-1.9.2-rc1 > 2.1*3
=> 6.300000000000001

Even though I realize that the templating engine should not be messing
with the ruby pre-defined precisions, I would like to ask what would be
the recommended way to get all ruby versions to behave the same?

For instance, I've noticed that in both 1.9.1 and 1.9.2-rc1 the
instruction (14/3.0).to_r returns the exact same rational, just
differing when using the #to_f

Best regards
--
Posted via http://www.ruby-forum.com/.

From: Robert Klemme on 13 Jul 2010 08:36
2010/7/13 Diogo Almeida <diogo.borges.almeida(a)gmail.com>:

> The Liquid templating engine has the following tests passing till ruby
> 1.9.2 rc1:
>
> assert_template_result "4.66666666666667", "{{ 14 | divided_by:'3.0' }}"
> #equals to 14/3.0 in irb
> assert_template_result "6.3", "{{ '2.1' | times:3 }}" #equals to 2.1*3
> in irb
>
> However, as far as I could understand, the float precision has been
> changed with RC1 and the first assertion now returns 15 decimal digits
> instead of 14:
> ruby-1.9.2-rc1 > 14/3.0
>  => 4.666666666666667
>
> And the second returns the same 15 decimal digits instead of 1:
> ruby-1.9.2-rc1 > 2.1*3
>  => 6.300000000000001
>
> Even though I realize that the templating engine should not be messing
> with the ruby pre-defined precisions, I would like to ask what would be
> the recommended way to get all ruby versions to behave the same?
>
> For instance, I've noticed that in both 1.9.1 and 1.9.2-rc1 the
> instruction (14/3.0).to_r returns the exact same rational, just
> differing when using the #to_f

I question the validity of the test. Expecting a particular
formatting of a float number without giving a concrete format is at
least fragile (as you have discovered) - I would even call it wrong.
Different than for integers there is no common agreed way to convert
floats to strings so if you want a particular formatting you need to
make it part of the test. An alternative would be a regexp match
against \A4\.6+7\z

irb(main):001:0> /\A4\.6+7\z/ =~ (14.0/3).to_s
=> 0

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

From: Diogo Almeida on 13 Jul 2010 09:15
Robert Klemme wrote:
> 2010/7/13 Diogo Almeida <diogo.borges.almeida(a)gmail.com>:
>
> I question the validity of the test. Expecting a particular
> formatting of a float number without giving a concrete format is at
> least fragile (as you have discovered) - I would even call it wrong.
> Different than for integers there is no common agreed way to convert
> floats to strings so if you want a particular formatting you need to
> make it part of the test. An alternative would be a regexp match
> against \A4\.6+7\z
>
> irb(main):001:0> /\A4\.6+7\z/ =~ (14.0/3).to_s
> => 0

Yes, I found it odd when I saw it myself. Though, since this was a
recent change I figured someone could know how to fallback to the "old
formatting", without having to use regex, or other alternative
approaches.

Best regards.
--
Posted via http://www.ruby-forum.com/.

From: Caleb Clausen on 13 Jul 2010 10:49
On 7/13/10, Diogo Almeida <diogo.borges.almeida(a)gmail.com> wrote:
> Robert Klemme wrote:
>> 2010/7/13 Diogo Almeida <diogo.borges.almeida(a)gmail.com>:
>>
>> I question the validity of the test. Expecting a particular
>> formatting of a float number without giving a concrete format is at
>> least fragile (as you have discovered) - I would even call it wrong.
>> Different than for integers there is no common agreed way to convert
>> floats to strings so if you want a particular formatting you need to
>> make it part of the test. An alternative would be a regexp match
>> against \A4\.6+7\z
>>
>> irb(main):001:0> /\A4\.6+7\z/ =~ (14.0/3).to_s
>> => 0
>
> Yes, I found it odd when I saw it myself. Though, since this was a
> recent change I figured someone could know how to fallback to the "old
> formatting", without having to use regex, or other alternative
> approaches.

1.9.2 has been changed so that float.to_s.to_f always round-trips with
a minimal string representation. This was not true in the past. This
new behavior is better; there's no flag or anything to get the old
behavior back. I suggest you follow Robert's suggestions for fixing
the test.

From: Diogo Almeida on 13 Jul 2010 14:30
Thanks guys
--
Posted via http://www.ruby-forum.com/.

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