Hi Yuri, Long time not seeing you ! welcome back :) Nice framework !
Esteban > On 18 Dec 2016, at 11:45, Юрий Мироненко <assargad...@gmail.com> wrote: > > Imagine, you have some object with amount and price variables. > And you want to calculate total, put this totals to collection and calculate > grand total. > > Naive implementation will be something like > total := amount * price for the first task > and something like > grandTotal := totals sum for the latter one. > > But what if amount or price are nil's? > You can add nil checks, of course: total := (amount ifNil:[0]) * (price > ifNil: [0]). > And then what if totals will be empty? More checks. > Is it really wise to have total to be zero if amount is nil? More > ifTrue:ifFalse: code. > And then you want to add amount := total / price calculation, and you realize > that both total and price may be nil, and price may be zero. > More and more and more checks. > > Protego (http://www.smalltalkhub.com/#!/~assargadon/Protego > <http://www.smalltalkhub.com/#!/~assargadon/Protego>) adds "protected" > versions of common operators and methods. > > So, you just put > total := amount *@ price > and > grandTotal := totals sum_protected > into your code - and everything just works. > > total will be nil if any of the operands are nil. grandTotal will be > calculated normally, even for empty totals collection (will return nil for > empty collection). > Collection can hold nil's and it will work anyway. If all elements of the > collection is nil, result will be nil. > > Protected version of addition and subtraction will treat nil's as zeros until > both operands are nil - then it will return nil. > There are protected versions of comparisions, too. > > It's quite simple idea, which is still very useful, and it makes code much > more readable, clean and self-commenting. > > That's why I have extracted this part of SmallPOS framework, and have > published it as separate package to use it in other, non-SmallPOS > applications.
