How to subclass Float class

> It looks like when I want to create a subclass of Float, I have this odd
> class creation message. Moreoever, I can add instance variable to this
> new class: when compiling there are wipe out: argument
> instanceVariableNames: '' remain empty.
>
> If I change Float to Object, all get back to normal.
>
> Why is it like this ?
>
>
> Float variableWordSubclass: #MyClass
> instanceVariableNames: ''
> classVariableNames: ''
> category: 'Cofigest-Financial'
>
>
> Thanks
>
> Hilaire
>

> Le 11/01/2015 09:06, stepharo a écrit :
>> Hilaire
>>
>> what is your requirement?
>>
>> Stef
>
> I want to create a currency object, basically a Float with an attribute
> to specify the currency unit.
>
> Hilaire
>
>

> Hilaire,
>
> unless you have very (very very) specific needs, I would strongly
> discourage you to use Float for anything related to Money or Percentages.
>
> We use a subclass of Object for MonetaryAmounts and implemented most
> of the protocol of Magnitude. But, most importantly, the amount
> instVar is made sure to always hold instances of ScaledDecimal (in VA
> Smalltalk, that is).
>
> Joachim
>
> Am 11.01.15 um 10:25 schrieb Hilaire:
>> Le 11/01/2015 09:06, stepharo a écrit :
>>> Hilaire
>>>
>>> what is your requirement?
>>>
>>> Stef
>>
>> I want to create a currency object, basically a Float with an attribute
>> to specify the currency unit.
>>
>> Hilaire
>>
>>
>
>
>

> Ah, I just saw on second reading that you want to implement something
> for currency exchange rates, not MonetaryAmounts. Still, don't use
> Float, use ScaledDecimal or FixedPoint and make sure it NEVER contains
> a Float. You'll get into all kinds of strange problems, starting with
> Imports from datasources like Yahoo or whatever.
>
> I'd subclass Object, and make the new class hold the exchange rates as
> a ScaledDecimal with a well-defined scale (like 4 or 6 or even 8
> digits if you want).
>
> Joachim
>
>
>
>
> Am 11.01.15 um 10:28 schrieb Joachim Tuchel:
>> Hilaire,
>>
>> unless you have very (very very) specific needs, I would strongly
>> discourage you to use Float for anything related to Money or
>> Percentages.
>>
>> We use a subclass of Object for MonetaryAmounts and implemented most
>> of the protocol of Magnitude. But, most importantly, the amount
>> instVar is made sure to always hold instances of ScaledDecimal (in VA
>> Smalltalk, that is).
>>
>> Joachim
>>
>> Am 11.01.15 um 10:25 schrieb Hilaire:
>>> Le 11/01/2015 09:06, stepharo a écrit :
>>>> Hilaire
>>>>
>>>> what is your requirement?
>>>>
>>>> Stef
>>>
>>> I want to create a currency object, basically a Float with an attribute
>>> to specify the currency unit.
>>>
>>> Hilaire
>>>
>>>
>>
>>
>>
>
>
>

> There are more arguments against Subclassing any Number class:
>
> Exchange rates are two-way most of the times. It is not only USD->EUR,
> but also the other way round. This is not the responsibilty of a number.
>
> For more information, I recommend Martin Fowler's Analysis Patterns book
> (old, but not dated at all!).
>
> Joachim
>
>
> Am 11.01.15 um 10:31 schrieb Joachim Tuchel:
>> Ah, I just saw on second reading that you want to implement something
>> for currency exchange rates, not MonetaryAmounts. Still, don't use
>> Float, use ScaledDecimal or FixedPoint and make sure it NEVER contains
>> a Float. You'll get into all kinds of strange problems, starting with
>> Imports from datasources like Yahoo or whatever.
>>
>> I'd subclass Object, and make the new class hold the exchange rates as
>> a ScaledDecimal with a well-defined scale (like 4 or 6 or even 8
>> digits if you want).
>>
>> Joachim
>>
>>
>>
>>
>> Am 11.01.15 um 10:28 schrieb Joachim Tuchel:
>>> Hilaire,
>>>
>>> unless you have very (very very) specific needs, I would strongly
>>> discourage you to use Float for anything related to Money or
>>> Percentages.
>>>
>>> We use a subclass of Object for MonetaryAmounts and implemented most
>>> of the protocol of Magnitude. But, most importantly, the amount
>>> instVar is made sure to always hold instances of ScaledDecimal (in VA
>>> Smalltalk, that is).
>>>
>>> Joachim
>>>
>>> Am 11.01.15 um 10:25 schrieb Hilaire:
>>>> Le 11/01/2015 09:06, stepharo a écrit :
>>>>> Hilaire
>>>>>
>>>>> what is your requirement?
>>>>>
>>>>> Stef
>>>>
>>>> I want to create a currency object, basically a Float with an attribute
>>>> to specify the currency unit.
>>>>
>>>> Hilaire
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>

> Joachim,
>
> Thanks for the tips.
> I saw the Unit package was following the same pattern you are describing.
> My first though was to use ScaledDecimal, but I discovered it is pretty
> slow with computation (amortization schedule, search for rate) but there
> are workarounds for that.
>
> Hilaire
>
> Le 11/01/2015 10:36, Joachim Tuchel a écrit :
>> There are more arguments against Subclassing any Number class:
>>
>> Exchange rates are two-way most of the times. It is not only USD->EUR,
>> but also the other way round. This is not the responsibilty of a number.
>>
>> For more information, I recommend Martin Fowler's Analysis Patterns book
>> (old, but not dated at all!).
>>
>> Joachim
>>
>>
>> Am 11.01.15 um 10:31 schrieb Joachim Tuchel:
>>> Ah, I just saw on second reading that you want to implement something
>>> for currency exchange rates, not MonetaryAmounts. Still, don't use
>>> Float, use ScaledDecimal or FixedPoint and make sure it NEVER contains
>>> a Float. You'll get into all kinds of strange problems, starting with
>>> Imports from datasources like Yahoo or whatever.
>>>
>>> I'd subclass Object, and make the new class hold the exchange rates as
>>> a ScaledDecimal with a well-defined scale (like 4 or 6 or even 8
>>> digits if you want).
>>>
>>> Joachim
>>>
>>>
>>>
>>>
>>> Am 11.01.15 um 10:28 schrieb Joachim Tuchel:
>>>> Hilaire,
>>>>
>>>> unless you have very (very very) specific needs, I would strongly
>>>> discourage you to use Float for anything related to Money or
>>>> Percentages.
>>>>
>>>> We use a subclass of Object for MonetaryAmounts and implemented most
>>>> of the protocol of Magnitude. But, most importantly, the amount
>>>> instVar is made sure to always hold instances of ScaledDecimal (in VA
>>>> Smalltalk, that is).
>>>>
>>>> Joachim
>>>>
>>>> Am 11.01.15 um 10:25 schrieb Hilaire:
>>>>> Le 11/01/2015 09:06, stepharo a écrit :
>>>>>> Hilaire
>>>>>>
>>>>>> what is your requirement?
>>>>>>
>>>>>> Stef
>>>>> I want to create a currency object, basically a Float with an attribute
>>>>> to specify the currency unit.
>>>>>
>>>>> Hilaire
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>

> Hilaire
>
> you have also acancagua that support unit and conversion and aconcagua
> came out of a project dealing
> with money and trades.
>
> http://sdmeta.gforge.inria.fr/Teaching/CoursAnnecy/0506-M1-COO/
> read the two articles in there.
>
> Stef

> Very interesting reading.
>
> The formula in figure 1 is wrong as it is "composed" interest, and power
> should be used.
>
> rate := 10 % / 1 year
> terms := 6 months
>
> 100$ * (1 + rate) ^ terms
>
> So I wonder how the simplification as exposed in Fig. 4 goes in that
> case (rate should be transformed to 10/1200) and would be really
> interested if the model can fit the real situation: how the model can
> deduce rate per year should be adapted to rate per month without a prior
> knowledge of the formula meaning.
>
> In Smalltalkhub I see two Acomcagua packages, which one to use?
>
>
> Hilaire
>
>
> Le 11/01/2015 12:22, stepharo a écrit :
>> Hilaire
>>
>> you have also acancagua that support unit and conversion and aconcagua
>> came out of a project dealing
>> with money and trades.
>>
>> http://sdmeta.gforge.inria.fr/Teaching/CoursAnnecy/0506-M1-COO/
>> read the two articles in there.
>>
>> Stef
>

> ask the authors they are both in the pharo mailing-list.
>
> Le 11/1/15 16:25, Hilaire a écrit :
>> Very interesting reading.
>>
>> The formula in figure 1 is wrong as it is "composed" interest, and power
>> should be used.
>>
>> rate := 10 % / 1 year
>> terms := 6 months
>>
>> 100$ * (1 + rate) ^ terms
>>
>> So I wonder how the simplification as exposed in Fig. 4 goes in that
>> case (rate should be transformed to 10/1200) and would be really
>> interested if the model can fit the real situation: how the model can
>> deduce rate per year should be adapted to rate per month without a prior
>> knowledge of the formula meaning.
>>
>> In Smalltalkhub I see two Acomcagua packages, which one to use?
>>
>>
>> Hilaire
>>
>>
>> Le 11/01/2015 12:22, stepharo a écrit :
>>> Hilaire
>>>
>>> you have also acancagua that support unit and conversion and aconcagua
>>> came out of a project dealing
>>> with money and trades.
>>>
>>> http://sdmeta.gforge.inria.fr/Teaching/CoursAnnecy/0506-M1-COO/
>>> read the two articles in there.
>>>
>>> Stef
>>
>
>
>

>
> The Aconcagua package looks nicely designed and well test covered.
>
> Thanks
>
> Hilaire
>
> Le 11/01/2015 21:03, stepharo a écrit :
>> ask the authors they are both in the pharo mailing-list.
>>
>> Le 11/1/15 16:25, Hilaire a écrit :
>>> Very interesting reading.
>>>
>>> The formula in figure 1 is wrong as it is "composed" interest, and power
>>> should be used.
>>>
>>> rate := 10 % / 1 year
>>> terms := 6 months
>>>
>>> 100$ * (1 + rate) ^ terms
>>>
>>> So I wonder how the simplification as exposed in Fig. 4 goes in that
>>> case (rate should be transformed to 10/1200) and would be really
>>> interested if the model can fit the real situation: how the model can
>>> deduce rate per year should be adapted to rate per month without a prior
>>> knowledge of the formula meaning.
>>>
>>> In Smalltalkhub I see two Acomcagua packages, which one to use?
>>>
>>>
>>> Hilaire
>>>
>>>
>>> Le 11/01/2015 12:22, stepharo a écrit :
>>>> Hilaire
>>>>
>>>> you have also acancagua that support unit and conversion and aconcagua
>>>> came out of a project dealing
>>>> with money and trades.
>>>>
>>>> http://sdmeta.gforge.inria.fr/Teaching/CoursAnnecy/0506-M1-COO/
>>>> read the two articles in there.
>>>>
>>>> Stef
>>
>>
>