Re: [RFC] [Discussion] Support object type in BCMath

On Fri, 29 Mar 2024, Jordan LeDoux wrote: > On Wed, Mar 27, 2024 at 12:08 AM Aleksander Machniak <alec@alec.pl> wrote: > > > On 27.03.2024 01:03, Saki Takamachi wrote: > > >> $num = new BcNum('1.23', 2); > > >> $result = $num + '1.23456'; > > >> $result->value; // '2.46456' > > >> $result->scale; // ?? > > > > > > In this case, $result->scale will be > > > '5'. I added this to the > > > RFC. > > > > I'm not sure I like this. Maybe we should be more strict here and > > treat the $scale in constructor (and later withScale()) as the > > actual scale for all operations. > > > > > For addition, it absolutely should expand scale like this, unless the > constructor also defines a default rounding type that is used in that > situation. All numbers, while arbitrary, will be finite, so addition > will always be exact and known based on inputs prior to calculation. > > Treating scale like this isn't more strict, it's confusing. For > instance: > > ``` > $numA = new Number('1.23', 2); > $numB = new Number('1.23456', 5); > > $expandedScale1 = $numA + $numB; // 2.46456 > $expandedScale2 = $numB + $numA; // 2.46456 > > $strictScale1 = $numA + $numB; // 2.46 assuming truncation > $strictScale2 = $numB + $numA; // 2.46456 > ``` > > I ran into this same issue with operand ordering when I was writing my > operator overload RFC. > > There are ways you could do the overload implementation that would get > around this for object + object operations, but it's also > mathematically unsound and probably unexpected for anyone who is going > to the trouble of using an arbitrary precision library. > > Addition and subtraction should automatically use the largest scale > from all operands. Division and multiplication should require a > specified scale. I agree. I think add/subtract also should always take the largest scale here. cheers, Derick