rspec users - Nov 2008 - any tricks re using " eql(5.5)", but where 5.5 is a decimal not float?

-- 
Sent from my mobile device

(woops - full email below)

Hi,

My rails migrations / mysql database uses Decimal and I''ve noticed in
my rspec when I do a "...should eql(5.5)" that they''re
failing as the
expected result here is a float not a decimal.  For example see
extract below:

     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)

What''s the best way of addressing this?  Is there trick regarding the
easiest way to address this?

Thanks




On Sat, Nov 8, 2008 at 9:18 AM, Greg Hauptmann
<greg.hauptmann.ruby at gmail.com> wrote:
> --
> Sent from my mobile device
>

On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
greg.hauptmann.ruby at gmail.com> wrote:
>
>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>
How about just expecting BigDecimal(''5.5'')?

///ark
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There''s my C roots showing. :) That should be
BigDecimal.new(''5.5''), of
course.

On Fri, Nov 7, 2008 at 3:47 PM, Mark Wilden <mark at mwilden.com> wrote:
> On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
> greg.hauptmann.ruby at gmail.com> wrote:
>
>>
>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>
>
> How about just expecting BigDecimal(''5.5'')?
>
> ///ark
>
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"Greg Hauptmann" <greg.hauptmann.ruby at gmail.com> writes:

Do you mean BigDecimal?  Anyway, you should probably be using == instead
of eql.
>> 5.5 == BigDecimal.new(''5.5'')
=> true
>> 5.5.eql? BigDecimal.new(''5.5'')
=> false

eql? is object identity and is generally not what you''re after.

Pat

On Fri, Nov 7, 2008 at 3:51 PM, Pat Maddox <pergesu at gmail.com> wrote:
> "Greg Hauptmann" <greg.hauptmann.ruby at gmail.com> writes:
>
> Do you mean BigDecimal?  Anyway, you should probably be using == instead
> of eql.
>
> >> 5.5 == BigDecimal.new(''5.5'')
> => true
> >> 5.5.eql? BigDecimal.new(''5.5'')
> => false
>
> eql? is object identity and is generally not what you''re after.
>
Yeah, but
>> BigDecimal(''5.5'').eql?
BigDecimal(''5.5'')
=> true

So it''s either creating value objects (like Symbol) or BigDecimal.eql?
doesn''t do object equality.

What''s interesting is that you can create BigDecimals this way (without
calling new). You can do it with Strings, too.
>> String(''asdf'')
=> "asdf"

But not everything:
>> Hash(:a => 5)
NoMethodError: undefined method `Hash'' for #<Object:0x3799c>
    from (irb):12

As Johnny Carson used to say, "I did not know that."

///ark
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in fact I guess I was fishing for an easier way than this...if one
exists?  or is ruby & rspec "eql()" just strict here in terms of
types?

On 11/7/08, Mark Wilden <mark at mwilden.com>
wrote:
> On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
> greg.hauptmann.ruby at gmail.com> wrote:
>
>>
>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>
>
> How about just expecting BigDecimal(''5.5'')?
>
> ///ark
>
-- 
Sent from my mobile device

On Fri, Nov 7, 2008 at 6:24 PM, Greg Hauptmann
<greg.hauptmann.ruby at gmail.com> wrote:
> (woops - full email below)
>
> Hi,
>
> My rails migrations / mysql database uses Decimal and I''ve noticed
in
> my rspec when I do a "...should eql(5.5)" that they''re
failing as the
> expected result here is a float not a decimal.  For example see
> extract below:
>
>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>
> What''s the best way of addressing this?  Is there trick regarding
the
> easiest way to address this?
You aren''t by chance using decimals to represent money are you?

-- 
Zach Dennis
http://www.continuousthinking.com
http://www.mutuallyhuman.com

yep - this was recommended on forums over float - why?

On Sat, Nov 8, 2008 at 11:48 AM, Zach Dennis <zach.dennis at gmail.com>
wrote:
> On Fri, Nov 7, 2008 at 6:24 PM, Greg Hauptmann
> <greg.hauptmann.ruby at gmail.com> wrote:
>> (woops - full email below)
>>
>> Hi,
>>
>> My rails migrations / mysql database uses Decimal and I''ve
noticed in
>> my rspec when I do a "...should eql(5.5)" that
they''re failing as the
>> expected result here is a float not a decimal.  For example see
>> extract below:
>>
>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>
>> What''s the best way of addressing this?  Is there trick
regarding the
>> easiest way to address this?
>
> You aren''t by chance using decimals to represent money are you?
>
> --
> Zach Dennis
> http://www.continuousthinking.com
> http://www.mutuallyhuman.com
> _______________________________________________
> rspec-users mailing list
> rspec-users at rubyforge.org
> http://rubyforge.org/mailman/listinfo/rspec-users
>

On Fri, Nov 7, 2008 at 9:12 PM, Greg Hauptmann
<greg.hauptmann.ruby at gmail.com> wrote:
> yep - this was recommended on forums over float - why?
You are in for a lot of headaches in you application resorting to
decimal fields in the database, since it restores them as BigDecimals.
It sucks to deal with BigDecimals in your app. I very highly recommend
the Money library. I recommend installing it as a plugin and using the
CollectiveIdea fork.

http://github.com/collectiveidea/money/tree/master

Even if all you do is take 20 minutes to check out the Money library
in a dummy app, I think you will be glad you did.

Zach

>
> On Sat, Nov 8, 2008 at 11:48 AM, Zach Dennis <zach.dennis at
gmail.com> wrote:
>> On Fri, Nov 7, 2008 at 6:24 PM, Greg Hauptmann
>> <greg.hauptmann.ruby at gmail.com> wrote:
>>> (woops - full email below)
>>>
>>> Hi,
>>>
>>> My rails migrations / mysql database uses Decimal and I''ve
noticed in
>>> my rspec when I do a "...should eql(5.5)" that
they''re failing as the
>>> expected result here is a float not a decimal.  For example see
>>> extract below:
>>>
>>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>>
>>> What''s the best way of addressing this?  Is there trick
regarding the
>>> easiest way to address this?
>>
>> You aren''t by chance using decimals to represent money are
you?
>>
>> --
>> Zach Dennis
>> http://www.continuousthinking.com
>> http://www.mutuallyhuman.com
>> _______________________________________________
>> rspec-users mailing list
>> rspec-users at rubyforge.org
>> http://rubyforge.org/mailman/listinfo/rspec-users
>>
>


-- 
Zach Dennis
http://www.continuousthinking.com
http://www.mutuallyhuman.com

"Greg Hauptmann" <greg.hauptmann.ruby at gmail.com> writes:
> in fact I guess I was fishing for an easier way than this...if one
> exists?  or is ruby & rspec "eql()" just strict here in terms
of
> types?
>
> On 11/7/08, Mark Wilden <mark at mwilden.com> wrote:
>> On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
>> greg.hauptmann.ruby at gmail.com> wrote:
>>
>>>
>>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>>
>>
>> How about just expecting BigDecimal(''5.5'')?
>>
>> ///ark
>>
I''m not sure if you got my email before, but 6.5
=BigDecimal.new(''6.5'').  So use == instead and you should be
good.

Pat

thanks Pat - yes I missed it when reading your email - I''d been using
".eql" for everything....thanks

On Sat, Nov 8, 2008 at 2:10 PM, Pat Maddox <pergesu at gmail.com>
wrote:
> "Greg Hauptmann" <greg.hauptmann.ruby at gmail.com> writes:
>
>> in fact I guess I was fishing for an easier way than this...if one
>> exists?  or is ruby & rspec "eql()" just strict here in
terms of
>> types?
>>
>> On 11/7/08, Mark Wilden <mark at mwilden.com> wrote:
>>> On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
>>> greg.hauptmann.ruby at gmail.com> wrote:
>>>
>>>>
>>>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>>>
>>>
>>> How about just expecting BigDecimal(''5.5'')?
>>>
>>> ///ark
>>>
>
> I''m not sure if you got my email before, but 6.5 =>
BigDecimal.new(''6.5'').  So use == instead and you should be
good.
>
> Pat
> _______________________________________________
> rspec-users mailing list
> rspec-users at rubyforge.org
> http://rubyforge.org/mailman/listinfo/rspec-users
>

very bizzare but whilst I needed to use this approach to fix one of my
tests, I realised the test before was working without having to make
it a big decimal - go figure   :)

  --------------------------------
  it "should return last IR when date > last interest rate" do
    @source_bank.ir(Time.now.to_date + 1.years).should == 8.5  # <== WORKED
FINE
  end

  it "should return latest IR not greater than date specified when a
date is passed" do
    @source_bank.ir(Time.now.to_date + 8.days).should
=BigDecimal.new(''6.5'') # <== NEEDED TO USE BigDecimal here
  end
  --------------------------------


On Sat, Nov 8, 2008 at 3:37 PM, Greg Hauptmann
<greg.hauptmann.ruby at gmail.com> wrote:
> thanks Pat - yes I missed it when reading your email - I''d been
using
> ".eql" for everything....thanks
>
> On Sat, Nov 8, 2008 at 2:10 PM, Pat Maddox <pergesu at gmail.com>
wrote:
>> "Greg Hauptmann" <greg.hauptmann.ruby at gmail.com>
writes:
>>
>>> in fact I guess I was fishing for an easier way than this...if one
>>> exists?  or is ruby & rspec "eql()" just strict here
in terms of
>>> types?
>>>
>>> On 11/7/08, Mark Wilden <mark at mwilden.com> wrote:
>>>> On Fri, Nov 7, 2008 at 3:24 PM, Greg Hauptmann <
>>>> greg.hauptmann.ruby at gmail.com> wrote:
>>>>
>>>>>
>>>>>     expected 6.5, got
#<BigDecimal:23d8284,''0.65E1'',8(8)> (using .eql?)
>>>>>
>>>>
>>>> How about just expecting BigDecimal(''5.5'')?
>>>>
>>>> ///ark
>>>>
>>
>> I''m not sure if you got my email before, but 6.5 =>>
BigDecimal.new(''6.5'').  So use == instead and you should be
good.
>>
>> Pat
>> _______________________________________________
>> rspec-users mailing list
>> rspec-users at rubyforge.org
>> http://rubyforge.org/mailman/listinfo/rspec-users
>>
>

On Nov 08, 2008, at 2:18 am, Zach Dennis wrote:
> <greg.hauptmann.ruby at gmail.com> wrote:
>> yep - this was recommended on forums over float - why?
>
> You are in for a lot of headaches in you application resorting to
> decimal fields in the database, since it restores them as BigDecimals.
> It sucks to deal with BigDecimals in your app. I very highly recommend
> the Money library. I recommend installing it as a plugin and using the
> CollectiveIdea fork.

Ha, I wrote the ActiveRecord patch so this was possible :)

The reason for storing monetary values as SQL decimals is that they  
aren''t subject to rounding errors[1].  I used to work in the finance  
sector, and it was absolutely unacceptable to expose financial  
calculations to these errors.  Hence I added support in ActiveRecord  
so we could use Rails; it was just not an option otherwise.

The decision you have to make is between the extra effort now of using  
decimals in your code vs the extra effort later of explaining to your  
users why your calculations sometimes come out wrong.  And that  
depends on how much your users value knowing that these figures are  
correct.

Ashley


[1] http://www.theregister.co.uk/2006/08/12/floating_point_approximation/

-- 
http://www.patchspace.co.uk/
http://aviewfromafar.net/

Ashley - what''s you''re recommendation re using BigDecimal
(which does
work as you point out) and the Money gem (which it sounds like makes a
dev''s life a bit easier)???  Is it worth trying to port an application
from use of BigDecimal to Money gem???

On Sun, Nov 9, 2008 at 10:27 PM, Ashley Moran
<ashley.moran at patchspace.co.uk> wrote:
>
> On Nov 08, 2008, at 2:18 am, Zach Dennis wrote:
>
>> <greg.hauptmann.ruby at gmail.com> wrote:
>>>
>>> yep - this was recommended on forums over float - why?
>>
>> You are in for a lot of headaches in you application resorting to
>> decimal fields in the database, since it restores them as BigDecimals.
>> It sucks to deal with BigDecimals in your app. I very highly recommend
>> the Money library. I recommend installing it as a plugin and using the
>> CollectiveIdea fork.
>
>
> Ha, I wrote the ActiveRecord patch so this was possible :)
>
> The reason for storing monetary values as SQL decimals is that they
aren''t
> subject to rounding errors[1].  I used to work in the finance sector, and
it
> was absolutely unacceptable to expose financial calculations to these
> errors.  Hence I added support in ActiveRecord so we could use Rails; it
was
> just not an option otherwise.
>
> The decision you have to make is between the extra effort now of using
> decimals in your code vs the extra effort later of explaining to your users
> why your calculations sometimes come out wrong.  And that depends on how
> much your users value knowing that these figures are correct.
>
> Ashley
>
>
> [1] http://www.theregister.co.uk/2006/08/12/floating_point_approximation/
>
> --
> http://www.patchspace.co.uk/
> http://aviewfromafar.net/
>
> _______________________________________________
> rspec-users mailing list
> rspec-users at rubyforge.org
> http://rubyforge.org/mailman/listinfo/rspec-users
>

On Nov 10, 2008, at 12:21 am, Greg Hauptmann wrote:
> Ashley - what''s you''re recommendation re using BigDecimal
(which does
> work as you point out) and the Money gem (which it sounds like makes a
> dev''s life a bit easier)???  Is it worth trying to port an
application
> from use of BigDecimal to Money gem???

Hi Greg

I''d use the money gem if and only if it''s underlying
implementation is
BigDecimal or some other fixed-precision system.  I''ve had a look over
it and it appears to use integers to store values as small as 1/100 of  
the base unit.  So as long as you don''t need to use anything smaller  
than that in calculations (ie, you only add, and never multiply,  
values - eg for tax calculations) it will be fine.

I''ll try not to say too much more, we''re straying well away
from RSpec
territory...

Ashley

-- 
http://www.patchspace.co.uk/
http://aviewfromafar.net/