August 2019 - Pharo-users - lists.pharo.org

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Richard O'Keefe

https://github.com/rwobben/bankaccount points to a repository with C# code, so I cannot comment on the Smalltalk. There is, however, a striking thing about the C# code, qua C#, that is worth mentioning. It is not encapsulated. Let's start with the most obvious one. A bank account has a password, and you are supposed to provide the right password in order to get information from it. Your interface *reveals* the password, so malicious code can do var pass = theBankAccount.password; and then provide the password back. What's needed is something like var balance = theBankAccount.queryBalance(pass); where passwords go *in* to theBankAccount but never ever ever come *out*. Another thing is that a BankAccount belongs to a specific Customer. There's a good way and a bad way to manage this. The bad way is for the caller to create a new account that belongs to nobody, and then *tell* the Customer "here is a new account". With this interface, you could tell any number of Customers that they own the account. That's possible in the real world, but in the challenge, it isn't. The good way is to *ask* the Customer "please create a new account and tell me what it is", and have no way to force a Customer to accept an account willy nilly. That way a Customer can be certain that the accounts it is holding belong to it and it alone. Or it could be were it not for a major encapsulation issue. The idea of encapsulation is that EVERY CHANGE TO AN OBJECT'S STATE MUST BE MADE BY THAT OBJECT including the start of owned containers. In Java, for example, you might have public class Customer { private final ArrayList<Account> accounts = new ArrayList<Account>(); ... public List<Account> getAccounts() { return Collections.unmodifiableList(accounts); } ... public Account newAccount(...details...) { final Account a = new Account(...details...'); accounts.add(a); return a; } ... } If you are going to provide access to a collection, (1) make the collection immutable in the first place, or (2) return an immutable view of it, or (3) best of all, DON'T provide access to the collection but provide queries that extract just the information you want to make available. This has nothing to do with Java or Smalltalk or C# as such; encapsulation is object-oriented-programming 102. For what it's worth, I used to be a University lecturer, and it was MUCH harder for students to grasp encapsulation than to grasp recursion. I have no idea why. Just pretend that you are a nice little object surrounded by malevolent pranksters who can force you to do anything in your interface, and make sure they cannot harm you. Oh, when I asked about the source of the challenge, what I was getting at was "is this your paraphrase of the challenge, in which case please tell us to find the original, or is this the actual unmodified original text, in which case --ing h---, you have my profound sympathy." This looks like a garbled version of an exercise that I did a little over 10 years ago, which I found in a Java-based book whose details I unfortunately forgot to record. Right down to the names of the classes! That is why I am pretty sure that there is a description of the problem somewhere that makes sense.

Aug. 17, 2019

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Roelof Wobben

Aug. 17, 2019

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Richard O'Keefe

What is the source of the challenge? Is there a version in English? I am having very serious trouble trying to make sense of "your bank accounts can have multiple accounts for money". I note that in your C# code a customer has an ID, a first name, and a last name. There is nothing about this in the challenge text, and since some people have one-part names, I have a three- part name, and my father had and my grand-daughter has four-part names, I should think that simply representing a name as a string without caring about subdivisions would be better. What I'm getting at is this: with a specification like that, how will you know when your code is correct?

Aug. 17, 2019

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Richard O'Keefe

What did you expect transaction = Transactions new. to do, besides computing the answer 'false' and throwing it away? On Fri, 16 Aug 2019 at 22:38, Roelof Wobben <r.wobben(a)home.nl> wrote: > Hello, > > I try now to make this challege work on Pharo which is orginal a c# > problem to practice OOP. > > The challenge is this : > > Consider the following situation: > You have a bank account. Bank account has a password which is hidden and you can access data within bank > account only by providing the right credentials. > Bank acount has a whole bunch of transaction history. > Transaction is basically a record with name, description, amount (either positive or negative) > and specific account linked to it (your bank accounts can have multiple accounts for money). > > You need to: ask each user for credentials and output how much money do they have in each bank account. > > Classes: Customer, Transaction, BankAccount. > > So far I have this : https://github.com/rwobben/bankaccount > > but when I do this on playground: > > customer := Customer new. > bankAccount := Bankaccounts new. > bankAccount password: 'secret'. > customer AddBankAccountToCustomer: bankAccount. > > transaction = Transactions new. > bankAccount addToBankAccount: transaction. > > customer. > > > and I inspect the customer I do not see the transaction addded to the bankaccounts collection. > > What do I do wrong ? > > Roelof > > > > >

Aug. 17, 2019

2 days left to submit your software to the ESUG Innovation Technology Awards

by N. Bouraqadi

Submit your project and show all the cool things enabled by Smalltalk :-) > Begin forwarded message: > > From: "N. Bouraqadi" <bouraqadi(a)gmail.com <mailto:bouraqadi@gmail.com>> > Subject: ESUG Innovation Technology Awards Call for submissions > Date: 9 July 2019 at 16:08:49 CEST > To: Board ESUG <board(a)lists.esug.org <mailto:board@lists.esug.org>>, Any question about pharo is welcome <pharo-users(a)lists.pharo.org <mailto:pharo-users@lists.pharo.org>> > > Dear Smalltalkers, > > Developers are invited to submit their Smalltalk-related project to the 16th edition of the ESUG Innovation Technology Awards. > The top 3 teams with the most innovative software will receive, respectively, 500 Euros, 300 Euros and 200 Euros. > > Submit now! > > Instructions are available at: https://esug.github.io/2019-Conference/awardsCall2019.html <https://esug.github.io/2019-Conference/awardsCall2019.html> > > Noury

Aug. 16, 2019

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Roelof Wobben

Aug. 16, 2019

Re: [Pharo-users] Why do I not see the transactions when opening a customer

by Ben Coman

> > and I inspect the customer I do not see the transaction added to the bankaccounts collection. > > Rather than focus on what you don't see. What do you see? And does anything look odd about it? cheers -ben

Aug. 16, 2019

Why do I not see the transactions when opening a customer

by Roelof Wobben

Aug. 16, 2019

Re: [Pharo-users] Garage

by Sven Van Caekenberghe

Jeff, > On 15 Aug 2019, at 23:36, Jeff Gray <jeff(a)rogerthedog.com> wrote: > > Is anyone maintaining garage? I get some errors in Pharo 7, which I have > patched as I have needed to. Looked in the GitHub repository and last update > was back in September. Garage is a community project with no particular maintainer. This means that we (the users) should all try to maintain it. If you have fixes or improvements, please submit PRs. Sven

Aug. 16, 2019

Re: [Pharo-users] finds replacements for deprecated objects

by Ben Coman

On Thu, 15 Aug 2019 at 09:37, Steve Quezadas <steveeq1(a)gmail.com> wrote: > Forgive the naive question here. But if an object gets deprecated, how do > you find the closest replacement object in Pharo? Is there a way to do it > within the VM or do you just have to check the documentation? > Hi Steve, First I just like to check the language you're using. The usual discussion I see about deprecation relates to "classes" that define the objects rather than the "objects" themselves. Do you mean "if a class gets deprecated?" Also the "VM" is compiled with a C-compiler (gcc or clang) and not code that most Pharo users will ever look at. Different to other languages (e.g. Java), the Pharo VM contains only low-level routines for memory-manipulation, bytecode-execution and a few primitives for interfacing different operating systems libraries. 90% of Pharo library code is stored "within the Image" that runs on top of the VM. So if you want to find the replacement for SomeDeprecatedClass that your application is using, a bit of investigation in the old Image should be able to discover places its being used in the default Pharo libraries, the look at those same places in the latest Image and see which class they are now using. Two useful tools for that in SystemBrowser are: 1. Right-click a class and choose "Analyse > Class refs" 2. Right-click a method and choose "Senders" Pharo also has some facilities for creation of deprecation-rules to automatically identify deprecation-use by your code and suggest the replacement. Whether those have been written for the particular thing you are interested in is another question. Do you have a particular class or method in mind? And which versions of Pharo are you considering? cheers -ben

Aug. 16, 2019