http://smalltalkhub.com/pdebruic/Money/index.html
Am Mo., 30. Aug. 2021 um 14:51 Uhr schrieb jtuc...@objektfabrik.de < jtuc...@objektfabrik.de>: > Hi Sven, > > > I just tried 46.79 asScaledDecimal and 46.79 asScaledDecimal: 2 in both > VAST and Pharo and see quite different results. > In VAST, not providing a scale returns 46.79, but with a scale of 14 > (46.79s14). But it is still 46.79. > > What's good is that the results of "asScaledDecimal: 2" yields the same > results on VAST and Pharo. > > Your examples also use a fixed scale of 2. So is it safe to assume that > when you provide the scale, ScaledDecimal is good for monetary amounts > in Pharo? I ask because that is what I once learned in an IBM training > decades ago: use ScaledDecimals for money and percentages, never use > floats. > > Would you agree that as a rule of thumb, Pounds, Dollars and Euros are > safely stored and processed when you make sure to always provide the > scale of 2 (unless you manage stock or petrol prices which use 3 or 4 or > even more digits)? > > Joachim > > > > > > Am 30.08.21 um 14:31 schrieb Sven Van Caekenberghe: > > David, > > > >> On 30 Aug 2021, at 14:02, David Pennington <da...@totallyobjects.com> > wrote: > >> > >> Hi everyone. I have a little bank analysis package for my own use but > having trouble displaying and storing amounts. I parse out a CSV file from > the bank and convert the amounts from text to ScaledDecimal. I then store > these into a STON file, which converts them back to text. I then read them > in and convert them back to ScaledDecimal again. > >> > >> I am not used to ~Pharo have spent 24 years using VisualAge Smalltalk > so I need a little bit of help because I am getting 1 Penny errors in the > conversions. I can cope with this but I would like to get it right. > >> > >> Can anyone give me a simple means of managing, say, an amount like > £76.49 from the bank so that it stops coming back to me as £76.48? > >> > >> David > >> Totally Objects > > Working with money is always challenging. I know that many people say > 'Use ScaledDecimal' as if that magically solves all problems but it does > not. ScaledDecimal is a bit of a dangerous class to use. It is just a > fraction with a certain precision. Internally it might be pretty accurate > with respect to most operations, its external representation as floating > point number can be misleading, as this representation is prone to all > problems related to floating point (including the fact that decimal and > binary floating point are not the same). > > > > STON does not doing anything wrong as far as I know. Consider the > following: > > > > | amount ston | > > amount := 76.49 asScaledDecimal. > > ston := STON toString: amount. > > STON fromString: ston. > > (STON fromString: ston) = amount. > > "true" > > > > | amount ston | > > amount := 76.49 asScaledDecimal: 2. > > ston := STON toString: amount. > > STON fromString: ston. > > (STON fromString: ston) = amount. > > "true" > > > > | amount ston | > > amount := 76.49. > > ston := STON toString: amount. > > STON fromString: ston. > > (STON fromString: ston) = amount. > > "true" > > > > BUT, 76.49 asScaledDecimal already has your penny loss (if rounded to > pennies). > > > > HTH, > > > > Sven > > > > -- > ----------------------------------------------------------------------- > Objektfabrik Joachim Tuchel mailto:jtuc...@objektfabrik.de > Fliederweg 1 http://www.objektfabrik.de > D-71640 Ludwigsburg http://joachimtuchel.wordpress.com > Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1 > >
