I come from a currency trader background and way back in 1983, I was dealing with this in North Star Basic and then UCSD Pascal and into VisualSmalltalk (remember that?) so I have some history here. Trouble is, at 76, my little grey cells are letting me down bit. Excuses over. I will go back into the code and make sure that I scale all these ScaledDecimals to 2 and see if that helps.
BTW, I wasn’t suggesting that there was any problem with STON as that works brilliantly for me. David > On 30 Aug 2021, at 13:51, jtuc...@objektfabrik.de wrote: > > 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 >
