"Sum" is usually well-defined, so I don't understand what the block's for. With the block it's more like "take this collection, map the values with some function, and sum the result".
If so, it sounds like you're looking for a sugared form of (myCollection collect: aBlock) inject: self first class zero into: #+. ? (There's already Float class >> #zero and (in Squeak at least) Integer class >> #zero, and so on. Just add MyUnit class >> #zero and you're done.) frank On 22 April 2013 10:37, Tudor Girba <tu...@tudorgirba.com> wrote: > Hi, > > I am CC-ing the pharo mailing list because it can be of interest. > > I agree with Guillaume that there is a legitimate need for a generic > solution. However, at the same time we lose the convenience of simply adding > numbers, which is likely to be the most encountered use case. > > I see a couple of possibilities: > - add Collection>>sum: aBlock from: aZeroValue that takes aZeroValue as the > default. > - add Collection>>sumNumbers: aBlock that takes 0 as default rather than > anyOne. > > What do you think? > > Cheers, > Doru > > > > On Mon, Apr 22, 2013 at 10:14 AM, Guillaume Larcheveque > <guillaume.larcheve...@gmail.com> wrote: >> >> For example, in Artefact we use Units and I have tried to use sum but it >> doesn't works because Units doesn't allow to do 0 + 4 cm which is >> inconsistent. >> >> >> 2013/4/22 Alexandre Bergel <alexandre.ber...@me.com> >>> >>> Thanks for letting us know. I cannot see a case where having 0 as the >>> initial value does not work as expected. >>> >>> Cheers, >>> Alexandre >>> >>> >>> Le 21 avr. 2013 à 17:35, Tudor Girba <tu...@tudorgirba.com> a écrit : >>> >>> > Hi, >>> > >>> > Pharo 2.0 comes with Collection>>sum: >>> > >>> > Collection>>sum: aBlock >>> > "This is implemented using a variant of the normal inject:into: >>> > pattern. >>> > The reason for this is that it is not known whether we're in the >>> > normal >>> > number line, i.e. whether 0 is a good initial value for the sum. >>> > Consider a collection of measurement objects, 0 would be the >>> > unitless >>> > value and would not be appropriate to add with the unit-ed objects." >>> > | sum sample | >>> > sample := aBlock value: self anyOne. >>> > sum := self inject: sample into: [ :previousValue :each | >>> > previousValue + (aBlock value: each) ]. >>> > ^ sum - sample >>> > >>> > To some extent, this is more generic than the one we had in Moose that >>> > considered only numbers: >>> > Collection>>sum: aSymbolOrBlock >>> > ^ self >>> > inject: 0 >>> > into: [:sum :each | sum + (aSymbolOrBlock value: each)] >>> > >>> > >>> > However, with the Pharo 2.0 implementation the collection must not be >>> > empty, while the other implementation we get 0. If the collection is >>> > empty, >>> > you get an exception due to anyOne. >>> > >>> > This induced several errors in metric computations (like number of >>> > methods of a package when the package had no classes). These are now >>> > fixed, >>> > but I thought I would let you know just in case you want to rely on this >>> > method. >>> > >>> > I actually still believe we would benefit from a robust but more >>> > limited sum:. Perhaps we could have sumNumbers:. >>> > >>> > Cheers, >>> > Doru >>> > >>> > >>> > -- >>> > www.tudorgirba.com >>> > >>> > "If you can't say why something is relevant, >>> > it probably isn't." >>> > >>> > >>> > _______________________________________________ >>> > Moose-dev mailing list >>> > moose-...@iam.unibe.ch >>> > https://www.iam.unibe.ch/mailman/listinfo/moose-dev >>> >>> _______________________________________________ >>> Moose-dev mailing list >>> moose-...@iam.unibe.ch >>> https://www.iam.unibe.ch/mailman/listinfo/moose-dev >> >> >> >> >> -- >> Guillaume Larcheveque >> >> >> _______________________________________________ >> Moose-dev mailing list >> moose-...@iam.unibe.ch >> https://www.iam.unibe.ch/mailman/listinfo/moose-dev >> > > > > -- > www.tudorgirba.com > > "Every thing has its own flow"
