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Re: [Pharo-users] Can it do this way ?

by Richard O'Keefe

Everything Joachim Tuchel wrote about this is fine EXCEPT that this is an Exercism task, where Roelof has to implement an API that he is given and is not at liberty to do it right. Thanks to the way that IsbnVerifierTest is structured, - the IsbnVerifier class has NO use for ANY variables of ANY kind: no instance variables, no class variables, and no class instance variables. - the IsbnVerifier class has only ONE method that is called, and that is on the INSTANCE side. That is, it's a simple pure function disguised as an object. A good design might have an ISBN class, and would put #isValidISBN10: and #isValidISBN13: on the class side. But to solve the Exercism exercises, you HAVE to implement the API that the test class is expecting, not something better. If it passes the tests, it is by definition right. If it doesn't, it is by definition wrong, even if it is a far better design. So - one class, IsbnVerifier - with no variables of any kind - with one and only one method, #isValidIsbn, on the instance side. It all gets so much clearer when you realise that the Exercism tasks are NOT designed to teach Object-Oriented Design. The problems have to serve many programming languages, some of which, like bash and x86 assembly code, are not object-oriented. On Wed, 2 Sep 2020 at 18:42, jtuchel(a)objektfabrik.de < jtuchel(a)objektfabrik.de> wrote: > Roelof, > > I don't think so. > > A Class cannot access instance variables. Why? because a Class doesn't > know which of its instances to ask for it. > Ask yourself: who is "self" in a Class method? Is it the Class or is it an > individual instance of the Class? > > (Hint: in a Class, #self is the Class, while in an instance, #self is the > instance) . > > > "Who" do you want to validate the ISBN number? An individual instance of > your Class (like Book)? Or is validating an ISBNNumber a Task that is > independent of an individual item? If it is independent, then why would you > want to use semething specific in that method? > > You need to understand the differences between Class and Instance > variables. I suggest reading Chapter 4 of "The Art and Science of > Smalltalk > <http://stephane.ducasse.free.fr/FreeBooks/Art/artAdded174186187Final.pdf>" > or better: read the whole book. It's easy to read and sparks quite a few > A-HA's per hour. > > > HTH > > Joachim > > > Am 02.09.20 um 08:18 schrieb Roelof Wobben: > > Hello, > > I have now a challenge where I have to validate a ISBN number. > > Can I do something like this on the class side : > > (string isEmpty) > ifTrrue: [ ^ false] > ifFalse: [ digits:= something. > controlDigit := something. > self validateISBNNumber] > > where on the validateISBNNumber I use the instance variables digits and > controlDigit to validate the ISBN number on the instance side. > > Roelof > > > > > > > > > > -- > ----------------------------------------------------------------------- > Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de <jtuchel(a)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 > > > >

Sept. 2, 2020

Re: [Pharo-users] Can it do this way ?

by jtuchel＠objektfabrik.de

Roelof, I don't think so. A Class cannot access instance variables. Why? because a Class doesn't know which of its instances to ask for it. Ask yourself: who is "self" in a Class method? Is it the Class or is it an individual instance of the Class? (Hint: in a Class, #self is the Class, while in an instance, #self is the instance) . "Who" do you want to validate the ISBN number? An individual instance of your Class (like Book)? Or is validating an ISBNNumber a Task that is independent of an individual item? If it is independent, then why would you want to use semething specific in that method? You need to understand the differences between Class and Instance variables. I suggest reading Chapter 4 of "The Art and Science of Smalltalk <http://stephane.ducasse.free.fr/FreeBooks/Art/artAdded174186187Final.pdf>" or better: read the whole book. It's easy to read and sparks quite a few A-HA's per hour. HTH Joachim Am 02.09.20 um 08:18 schrieb Roelof Wobben: > Hello, > > I have now a challenge where I have to validate a ISBN number. > > Can I do something like this on the class side : > > (string isEmpty) > Â Â ifTrrue: [ ^ false] > Â ifFalse:Â [ digits:= something. > Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â controlDigit := something. > Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â self validateISBNNumber] > > where on the validateISBNNumber I use the instance variables digits > and controlDigit to validate the ISBN number on the instance side. > > Roelof > > > > > > > > -- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@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

Sept. 2, 2020

Can it do this way ?

by Roelof Wobben

Hello, I have now a challenge where I have to validate a ISBN number. Can I do something like this on the class side : (string isEmpty) Â Â ifTrrue: [ ^ false] Â ifFalse:Â [ digits:= something. Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â controlDigit := something. Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â self validateISBNNumber] where on the validateISBNNumber I use the instance variables digits and controlDigit to validate the ISBN number on the instance side. Roelof

Sept. 2, 2020

Re: [Pharo-users] mentoring contined I hope

by Richard O'Keefe

Richard Sargent is giving good advice that you cannot use in Exercism. Your code MUST pass the exercism tests and that means it MUST NOT limit the hour or minute ranges. On Tue, 1 Sep 2020 at 08:58, Roelof Wobben via Pharo-users < pharo-users(a)lists.pharo.org> wrote: > > I would argue against that approach. Make it a requirement that a given > API must be used with correct values. > e.g. #hours:minutes: requires hours between 00 and 23 and minutes between > 00 and 59. > > If you want to convert equivalent time values, use a specific API. For > example, many time implementations publicly define a seconds-based API, > such as Time class>>#fromSeconds:. You can do the same with your > implementation with a class-side #fromMinutes: method. (The corresponding > instance methods would be #asSeconds and #asMinutes or something similar.) > > > > Moment, I do not know if I understand you right. > > so I would use the given method and use on the instance another function > that takes care of the converting to or a valid time object or for example > convert it to minutes and on display take care that a valid time is shown. > > Do I understand you right ? > > I send this personal because I cannot send to the mailing list according > to some spam list >

Sept. 2, 2020

Re: [Pharo-users] mentoring continued I hope

by Richard O'Keefe

Roelof explicitly said that this is for an Exercism exercise. That exercise defines the API (implicitly) in the test cases. Roelof has no choice about what the API is, his job is just to make the tests pass. Your ideas about how to design an API are good ones, it's just that Exercism says what to do. On Tue, 1 Sep 2020 at 05:01, Richard Sargent < richard.sargent(a)gemtalksystems.com> wrote: > On Sun, Aug 30, 2020 at 10:04 PM Roelof Wobben via Pharo-users < > pharo-users(a)lists.pharo.org> wrote: > >> Hello, >> >> I have this challenge from exercism : >> https://github.com/exercism/pharo-smalltalk/tree/master/exercises/clock >> >> and this function is given : >> >> hour: anInteger minute: anInteger2 >> self shouldBeImplemented >> >> >> Schould I make it on this class method work that the minutes will not >> exceed the 59 minutes >> So when for example when 70 min are given so hour:0 minute:70 it will >> be converted to hour: 1 minutes: 10 >> > > I would argue against that approach. Make it a requirement that a given > API must be used with correct values. > e.g. #hours:minutes: requires hours between 00 and 23 and minutes between > 00 and 59. > > If you want to convert equivalent time values, use a specific API. For > example, many time implementations publicly define a seconds-based API, > such as Time class>>#fromSeconds:. You can do the same with your > implementation with a class-side #fromMinutes: method. (The corresponding > instance methods would be #asSeconds and #asMinutes or something similar.) > > > or can I better do this on the instance side. >> >> Regards, >> >> Roelof >> >> >>

Sept. 2, 2020

Re: [Pharo-users] mentoring continued I hope

by Richard O'Keefe

I have always found it annoying that the exercism specifications do not spell things out, so you HAVE to read the tests to find out what you are supposed to do, which pretty much spoils the point of them BEING tests. In this case, we note that there is a test case where the number of hours is 100, and it is to be accepted as meaning '04'. There is also a test case where the number of minutes is 160 and it is to be taken as 40 minutes plus 2 hours. So the only way you can pass the tests is something like class methods for: 'instance creation' hours: h minutes: m ^self new setMinutesSinceMidnight: (h * 60 + m bitOr: 0) \\ 1440 methods for: 'private' setMinutesSinceMidnight: m minutesSinceMidnight := m. methods for: 'accessing' hour ^minutesSinceMidnight // 60 minute ^minutesSinceMidnight \\ 60 The only *checking* that is involved is that the hour and minute counts must be integers, which I used " bitOr: 0" to do. What's the best way to do thisE? As for where to do checking in general, put it as close to the encapsulation boundary as you reasonably can. If there is a PUBLIC method for changing the time on a Clock, you need to put the checking in that method. If (as here) a clock value is supposed to be immutable, put it in the instance creation method. On Mon, 31 Aug 2020 at 18:18, Roelof Wobben via Pharo-users < pharo-users(a)lists.pharo.org> wrote: > Hello, > > I have this challenge from exercism : > https://github.com/exercism/pharo-smalltalk/tree/master/exercises/clock > > and this function is given : > > hour: anInteger minute: anInteger2 > self shouldBeImplemented > > > Schould I make it on this class method work that the minutes will not > exceed the 59 minutes > So when for example when 70 min are given so hour:0 minute:70 it will > be converted to hour: 1 minutes: 10 > or can I better do this on the instance side. > > Regards, > > Roelof > > >

Sept. 2, 2020

Re: [Pharo-users] CV/OCR Library

by Tudor Girba

Hi, Indeed, we have an integration for OpenCV here: https://github.com/feenkcom/gt4opencv Cheers, Doru > On Aug 31, 2020, at 4:14 PM, StÃ©phane Ducasse <stephane.ducasse(a)inria.fr> wrote: > > I know that there is an openCV binding by https://twitter.com/DmitryMatveev > You have a binding in GT too. > > >> On 31 Aug 2020, at 14:40, Esteban Maringolo <emaringolo(a)gmail.com> wrote: >> >> Hi, >> >> Does anybody know if there is an OCR or some CV library available for Pharo? >> >> I would like to make an experiment with recognizing the content of >> some fixed size form, and of course I prefer to do it with Smalltalk >> whenever possible. >> >> Regards! >> >> Esteban A. Maringolo >> > > -------------------------------------------- > StÃ©phane Ducasse > http://stephane.ducasse.free.fr / http://www.pharo.org > 03 59 35 87 52 > Assistant: Aurore Dalle > FAX 03 59 57 78 50 > TEL 03 59 35 86 16 > S. Ducasse - Inria > 40, avenue Halley, > Parc Scientifique de la Haute Borne, BÃ¢t.A, Park Plaza > Villeneuve d'Ascq 59650 > France > -- feenk.com "Innovation comes in the least expected form. That is, if it is expected, it already happened."

Sept. 1, 2020

Re: mentoring contined I hope

by Roelof Wobben

Sept. 1, 2020

Re: mentoring contined I hope

by Roelof Wobben

Op 1-9-2020 om 21:11 schreef Richard Sargent: > You will discover an error when you write your tests, but that's fine. > It's why you write tests. :-) > > #validateTime:minute: is a poor name choice for a few reasons. > - there is no validation going on. Validation would report an error > for invalid data. > - there is nothing to suggest what the first argument is, the > counterpart to "minute:". > - it doesn't suggest there will be a new Time ("Clock") created. > - it's a "verb phrase" saying it will *do* something rather than > answer something (I'm being vague here. Sorry.) > > I suggest #normalizedForHour:minute:. > It explains that it will normalize the values and that it will answer > a normalized result (it still isn't great, as it doesn't explain what). > Perhaps better would be #newNormalizedForHour:minute:. > > Thanks, I think I found the error and solved it hour: anInteger minute: anInteger2 Â Â Â ^ self new Â Â Â Â Â Â hour: (anInteger2 // 60 + anInteger) % 24; Â Â Â Â Â Â minute: anInteger2 % 60; Â Â Â Â Â Â yourself instance side : printOn: aStream Â Â Â ^ aStream Â Â Â Â Â Â nextPutAll: self hour asTwoCharacterString; Â Â Â Â Â Â nextPut: $:; Â Â Â Â Â Â nextPutAll: self minute asTwoCharacterString and the tests are green now time to sleep and tomorrow time to figure out how to add and substract minutes. As I remember it right you gave already the answer to me somewhere in our conversation Roelof I

Sept. 1, 2020

Re: [Pharo-users] mentoring contined I hope

by Richard Sargent

"self is a Clock" is an imprecise statement. Did you mean that it is *an instance of* the Clock class or that it is *the *Clock class itself? On Tue, Sep 1, 2020 at 10:33 AM Roelof Wobben <r.wobben(a)home.nl> wrote: > Op 1-9-2020 om 19:21 schreef Richard Sargent: > > What is the value of *self* when the error occurred? The debugger should > show you this. > > > > self is a Clock > >

Sept. 1, 2020