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• Automount of external hard disk

  - by moose

  I have an Intenso 6002560 1TB Memory Station - an external hard disk. This hard disk gets connected via Y-USB cable. When I connect both USB-ends to my Notebook, it gets recognized by my Ubuntu 10.04.4 LTS system: moose@pc07:~$ lsusb [...] Bus 002 Device 005: ID 13fd:1840 Initio Corporation [...] and Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00065e10 Device Boot Start End Blocks Id System /dev/sda1 * 1 37810 303704064 83 Linux /dev/sda2 37810 38914 8864769 5 Extended /dev/sda5 37810 38914 8864768 82 Linux swap / Solaris Disk /dev/sdc: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0d6ea32a Device Boot Start End Blocks Id System /dev/sdc1 1 121601 976759008+ c W95 FAT32 (LBA) But it did not get mounted: moose@pc07:/dev$ mount -l /dev/sda1 on / type ext4 (rw,errors=remount-ro,user_xattr) proc on /proc type proc (rw,noexec,nosuid,nodev) none on /sys type sysfs (rw,noexec,nosuid,nodev) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) none on /dev type devtmpfs (rw,mode=0755) none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) none on /dev/shm type tmpfs (rw,nosuid,nodev) none on /var/run type tmpfs (rw,nosuid,mode=0755) none on /var/lock type tmpfs (rw,noexec,nosuid,nodev) none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev) gvfs-fuse-daemon on /home/moose/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=moose) However, I could mount it manually with mount -t vfat /dev/sdc1 /mnt/sdc1 as you can see here: moose@pc07:~$ mount -l /dev/sda1 on / type ext4 (rw,errors=remount-ro,user_xattr) proc on /proc type proc (rw,noexec,nosuid,nodev) none on /sys type sysfs (rw,noexec,nosuid,nodev) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) none on /dev type devtmpfs (rw,mode=0755) none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) none on /dev/shm type tmpfs (rw,nosuid,nodev) none on /var/run type tmpfs (rw,nosuid,mode=0755) none on /var/lock type tmpfs (rw,noexec,nosuid,nodev) none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev) gvfs-fuse-daemon on /home/moose/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=moose) /dev/sdc1 on /mnt/sdc1 type vfat (rw) edit: Another command: moose@pc07:~$ sudo blkid -o list device fs_type label mount point UUID ---------------------------------------------------------------------------------------------------------------------- /dev/sda1 ext4 / 45eb611b-517e-425b-8057-0391726cccd5 /dev/sda5 swap <swap> e9dc42f3-594c-4b62-874a-305eda5eed41 moose@pc07:~$ blkid -o list device fs_type label mount point UUID ---------------------------------------------------------------------------------------------------------------------- /dev/sda1 ext4 / 45eb611b-517e-425b-8057-0391726cccd5 /dev/sda5 swap <swap> e9dc42f3-594c-4b62-874a-305eda5eed41 /dev/sdc1 /mnt/sdc1 edit: another command: moose@pc07:~$ ls -l /dev/disk/by-uuid/ total 0 lrwxrwxrwx 1 root root 10 2012-09-30 09:31 45eb611b-517e-425b-8057-0391726cccd5 -> ../../sda1 lrwxrwxrwx 1 root root 10 2012-09-30 09:31 e9dc42f3-594c-4b62-874a-305eda5eed41 -> ../../sda5 Here is a link to a Launchpad question about this problem. But I would like it to mount automatically. What do I have to do?

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• Naming methods that do the same thing but return different types

  - by Konstantin Ð.

  Let's assume that I'm extending a graphical file chooser class (JFileChooser). This class has methods which display the file chooser dialog and return a status signature in the form of an int: APPROVE_OPTION if the user selects a file and hits Open /Save, CANCEL_OPTION if the user hits Cancel, and ERROR_OPTION if something goes wrong. These methods are called showDialog(). I find this cumbersome, so I decide to make another method that returns a File object: in the case of APPROVE_OPTION, it returns the file selected by the user; otherwise, it returns null. This is where I run into a problem: would it be okay for me to keep the showDialog() name, even though methods with that name — and a different return type — already exist? To top it off, my method takes an additional parameter: a File which denotes in which directory the file chooser should start. My question to you: Is it okay to call a method the same name as a superclass method if they return different types? Or would that be confusing to API users? (If so, what other name could I use?) Alternatively, should I keep the name and change the return type so it matches that of the other methods? public int showDialog(Component parent, String approveButtonText) // Superclass method public File showDialog(Component parent, File location) // My method

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• When are Getters and Setters Justified

  - by Winston Ewert

  Getters and setters are often criticized as being not proper OO. On the other hand most OO code I've seen has extensive getters and setters. When are getters and setters justified? Do you try to avoid using them? Are they overused in general? If your favorite language has properties (mine does) then such things are also considered getters and setters for this question. They are same thing from an OO methodology perspective. They just have nicer syntax. Sources for Getter/Setter Criticism (some taken from comments to give them better visibility): http://www.javaworld.com/javaworld/jw-09-2003/jw-0905-toolbox.html http://typicalprogrammer.com/?p=23 http://c2.com/cgi/wiki?AccessorsAreEvil http://www.darronschall.com/weblog/2005/03/no-brain-getter-and-setters.cfm http://www.adam-bien.com/roller/abien/entry/encapsulation_violation_with_getters_and To state the criticism simply: Getters and Setters allow you to manipulate the internal state of objects from outside of the object. This violates encapsulation. Only the object itself should care about its internal state. And an example Procedural version of code. struct Fridge { int cheese; } void go_shopping(Fridge fridge) { fridge.cheese += 5; } Mutator version of code: class Fridge { int cheese; void set_cheese(int _cheese) { cheese = _cheese; } int get_cheese() { return cheese; } } void go_shopping(Fridge fridge) { fridge.set_cheese(fridge.get_cheese() + 5); } The getters and setters made the code much more complicated without affording proper encapsulation. Because the internal state is accessible to other objects we don't gain a whole lot by adding these getters and setters. The question has been previously discussed on Stack Overflow: http://stackoverflow.com/questions/565095/java-are-getters-and-setters-evil http://stackoverflow.com/questions/996179

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• OO Design, how to model Tonal Harmony?

  - by David

  I have started to write a program in C++ 11 that would analyse chords, scales, and harmony. The biggest problem I am having in my design phase, is that the note 'C' is a note, a type of chord (Cmaj, Cmin, C7, etc), and a type of key (the key of Cmajor, Cminor). The same issue arises with intervals (minor 3rd, major 3rd). I am using a base class, Token, that is the base class for all 'symbols' in the program. so for example: class Token { public: typedef shared_ptr<Token> pointer_type; Token() {} virtual ~Token() {} }; class Command : public Token { public: Command() {} pointer_type execute(); } class Note : public Token; class Triad : public Token; class MajorTriad : public Triad; // CMajorTriad, etc class Key : public Token; class MinorKey : public Key; // Natural Minor, Harmonic minor,etc class Scale : public Token; As you can see, to create all the derived classes (CMajorTriad, C, CMajorScale, CMajorKey, etc) would quickly become ridiculously complex including all the other notes, as well as enharmonics. multiple inheritance would not work, ie: class C : public Note, Triad, Key, Scale class C, cannot be all of these things at the same time. It is contextual, also polymorphing with this will not work (how to determine which super methods to perform? calling every super class constructors should not happen here) Are there any design ideas or suggestions that people have to offer? I have not been able to find anything on google in regards to modelling tonal harmony from an OO perspective. There are just far too many relationships between all the concepts here.

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• Any language where every class instance is a class too?

  - by Dokkat

  Taking inspiration from Javascript prototypes, I had the idea of a language where every instance can be used as a class. Before I potentially reinvent the wheel, I would like to ask if there is a language already using this concept: //To declare a Class, extend the base class (in this case, Type) Type(Weapon,{price:0}); //Same syntax to inherit; simply extend the parent: Weapon(Sword,{price:3}); Weapon(Axe,{price:4}); Sword(Katana,{price:7}); Sword(Dagger,{price:3}); //And the same to create an instance: Katana(myKatana,{nickname:"Leon"}); myKatana.price; // 7 myKatana.nickname; // Leon // An operator to return children of a class; Sword_; // [Katana, Dagger] // An operator to return array of descendants; Sword__; // [Katana, Dagger, myKatana] // An operator to return array of parents; Sword^; // Weapon // Arrays can be used as elements Sword__.price += 1; //increases price of Sword's descendants by 1 mySword.price; //8 // And to access specific element (using its name instead of index) var name = "mySword" Katana_[name]; // [mySword] Katana_[name].nickname; // Leon Has this kind of approach been already studied/implemented?

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• OOP oriented PHP app source code samples and advice

  - by abel

  The day I have been dreading has arrived. I never felt OOP or good software design was important(I knew they were important, but I thought I could manage without them.). However having read otherwise almost everywhere on the interwebs, I started dreading the day when my client would ask me for new features in an existing app. The day has come and the pain is unbearable! I have never coded my PHP websites "properly"(PHP is my primary language and the bulk of my work. I am learning Python (using web2py)) I take care that the website doesn't fall apart in a daily use scenario. I code pages like I was creating a list of static html files with bits of "magic code" in each of them(this bugs me a lot). How do I make the whole app more or less a single object? For eg. How do I design the object model for an invoicing app? I use a lot of functions for doing any particular thing in the same fashion throughout the app(for eg. validation, generating ids, calculating taxes etc.). I know the basics of OOP in general. Can anyone point me to source code samples of functional apps written in php? Or can someone provide pointers so I can recode my existing apps in a more modular way.

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• Why is an anemic domain model considered bad in C#/OOP, but very important in F#/FP?

  - by Danny Tuppeny

  In a blog post on F# for fun and profit, it says: In a functional design, it is very important to separate behavior from data. The data types are simple and "dumb". And then separately, you have a number of functions that act on those data types. This is the exact opposite of an object-oriented design, where behavior and data are meant to be combined. After all, that's exactly what a class is. In a truly object-oriented design in fact, you should have nothing but behavior -- the data is private and can only be accessed via methods. In fact, in OOD, not having enough behavior around a data type is considered a Bad Thing, and even has a name: the "anemic domain model". Given that in C# we seem to keep borrowing from F#, and trying to write more functional-style code; how come we're not borrowing the idea of separating data/behavior, and even consider it bad? Is it simply that the definition doesn't with with OOP, or is there a concrete reason that it's bad in C# that for some reason doesn't apply in F# (and in fact, is reversed)? (Note: I'm specifically interested in the differences in C#/F# that could change the opinion of what is good/bad, rather than individuals that may disagree with either opinion in the blog post).

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• How do you encode Algebraic Data Types in a C#- or Java-like language?

  - by Jörg W Mittag

  There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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• From a DDD perspective is a report generating service a domain service or an infrastructure service?

  - by Songo

  Let assume we have the following service whose responsibility is to generate Excel reports: class ExcelReportService{ public String generateReport(String fileFormatFilePath, ResultSet data){ ReportFormat reportFormat = new ReportFormat(fileFormatFilePath); ExcelDataFormatterService excelDataFormatterService = new ExcelDataFormatterService(); FormattedData formattedData = excelDataFormatterService.format(data); ExcelFileService excelFileService = new ExcelFileService(); String reportPath= excelFileService.generateReport(reportFormat,formattedData); return reportPath; } } This is pseudo code for the service I want to design where: fileFormatFilePath: path to a configuration file where I'll keep the format of my excel file (headers, column widths, number of columns,..etc) data: the actual records returned from the database. This data can't be used directly coz I might need to make further calculations to the data before inserting them to the excel file. ReportFormat: Value object to hold the report format, has methods like getHeaders(), getColumnWidth(),...etc. ExcelDataFormatterService: a service to hold any logic that need to be applied to the data returned from the database before inserting it to the file. FormattedData: Value object the represents the formatted data to be inserted. ExcelFileService: a wrapper top the 3rd party library that generates the excel file. Now how do you determine whether a service is an infrastructure or domain service? I have the following 3 services here: ExcelReportService, ExcelDataFormatterService and ExcelFileService?

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• DB Schema for ACL involving 3 subdomains

  - by blacktie24

  Hi, I am trying to design a database schema for a web app which has 3 subdomains: a) internal employees b) clients c) contractors. The users will be able to communicate with each other to some degree, and there may be some resources that overlap between them. Any thoughts about this schema? Really appreciate your time and thoughts on this. Cheers! -- -- Table structure for table locations CREATE TABLE IF NOT EXISTS locations ( id bigint(20) NOT NULL, name varchar(250) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1; -- -- Table structure for table privileges CREATE TABLE IF NOT EXISTS privileges ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, resource_id int(11) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=10 ; -- -- Table structure for table resources CREATE TABLE IF NOT EXISTS resources ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, user_type enum('internal','client','expert') NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Table structure for table roles CREATE TABLE IF NOT EXISTS roles ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, type enum('position','department') NOT NULL, parent_id int(11) DEFAULT NULL, user_type enum('internal','client','expert') NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Table structure for table role_perms CREATE TABLE IF NOT EXISTS role_perms ( id int(11) NOT NULL AUTO_INCREMENT, role_id int(11) NOT NULL, privilege_id int(11) NOT NULL, mode varchar(250) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; -- -- Table structure for table users CREATE TABLE IF NOT EXISTS users ( id int(10) unsigned NOT NULL AUTO_INCREMENT, email varchar(255) NOT NULL, password varchar(255) NOT NULL, salt varchar(255) NOT NULL, type enum('internal','client','expert') NOT NULL, first_name varchar(255) NOT NULL, last_name varchar(255) NOT NULL, location_id int(11) NOT NULL, phone varchar(255) NOT NULL, status enum('active','inactive') NOT NULL DEFAULT 'active', PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ; -- -- Table structure for table user_perms CREATE TABLE IF NOT EXISTS user_perms ( id int(11) NOT NULL AUTO_INCREMENT, user_id int(11) NOT NULL, privilege_id int(11) NOT NULL, mode varchar(250) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; -- -- Table structure for table user_roles CREATE TABLE IF NOT EXISTS user_roles ( id int(11) NOT NULL, user_id int(11) NOT NULL, role_id int(11) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1;

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• Benefits of classic OOP over Go-like language

  - by tylerl

  I've been thinking a lot about language design and what elements would be necessary for an "ideal" programming language, and studying Google's Go has led me to question a lot of otherwise common knowledge. Specifically, Go seems to have all of the interesting benefits from object oriented programming without actually having any of the structure of an object oriented language. There are no classes, only structures; there is no class/structure inheritance -- only structure embedding. There aren't any hierarchies, no parent classes, no explicit interface implementations. Instead, type casting rules are based on a loose system similar to duck-typing, such that if a struct implements the necessary elements of a "Reader" or a "Request" or an "Encoding", then you can cast it and use it as one. Does such a system obsolete the concept of OOP? Or is there something about OOP as implemented in C++ and Java and C# that is inherently more capable, more maintainable, somehow more powerful that you have to give up when moving to a language like Go? What benefit do you have to give up to gain the simplicity that this new paradigm represents?

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• An ideal way to decode JSON documents in C?

  - by AzizAG

  Assuming I have an API to consume that uses JSON as a data transmission method, what is an ideal way to decode the JSON returned by each API resource? For example, in Java I'd create a class for each API resource then initiate an object of that class and consume data from it. for example: class UserJson extends JsonParser { public function UserJson(String document) { /*Initial document parsing goes here...*/ } //A bunch of getter methods . . . . } The probably do something like this: UserJson userJson = new UserJson(jsonString);//Initial parsing goes in the constructor String username = userJson.getName();//Parse JSON name property then return it as a String. Or when using a programming language with associative arrays(i.e., hash table) the decoding process doesn't require creating a class: (PHP) $userJson = json_decode($jsonString);//Decode JSON as key=>value $username = $userJson['name']; But, when I'm programming in procedural programming languages (C), I can't go with either method, since C is neither OOP nor supports associative arrays(by default, at least). What is the "correct" method of parsing pre-defined JSON strings(i.e., JSON documents specified by the API provider via examples or documentation)? The method I'm currently using is creating a file for each API resource to parse, the problem with this method is that it's basically a lousy version of the OOP method, as it looks exactly like the OOP method but doesn't provide any OOP benefits(e.g., can't pass an object of the parser, etc.). I've been thinking about encapsulating each API resource parser file in a publicly accessed structure(pointing all functions/publicly usable variables to the structure) then accessing the parser file code from within the structure(parser.parse(), parser.getName(), etc.). As this way looks a bit better than the my current method, it still just a rip off the OOP way, isn't it? Any suggestions for methods to parse JSON documents on procedural programming lanauges? Any comments on the methods I'm currently using(either 3 of them)?

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• Mocking concrete class - Not recommended

  - by Mik378

  I've just read an excerpt of "Growing Object-Oriented Software" book which explains some reasons why mocking concrete class is not recommended. Here some sample code of a unit-test for the MusicCentre class: public class MusicCentreTest { @Test public void startsCdPlayerAtTimeRequested() { final MutableTime scheduledTime = new MutableTime(); CdPlayer player = new CdPlayer() { @Override public void scheduleToStartAt(Time startTime) { scheduledTime.set(startTime); } } MusicCentre centre = new MusicCentre(player); centre.startMediaAt(LATER); assertEquals(LATER, scheduledTime.get()); } } And his first explanation: The problem with this approach is that it leaves the relationship between the objects implicit. I hope we've made clear by now that the intention of Test-Driven Development with Mock Objects is to discover relationships between objects. If I subclass, there's nothing in the domain code to make such a relationship visible, just methods on an object. This makes it harder to see if the service that supports this relationship might be relevant elsewhere and I'll have to do the analysis again next time I work with the class. I can't figure out exactly what he means when he says: This makes it harder to see if the service that supports this relationship might be relevant elsewhere and I'll have to do the analysis again next time I work with the class. I understand that the service corresponds to MusicCentre's method called startMediaAt. What does he mean by "elsewhere"? The complete excerpt is here: http://www.mockobjects.com/2007/04/test-smell-mocking-concrete-classes.html

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• Data classes: getters and setters or different method design

  - by Frog

  I've been trying to design an interface for a data class I'm writing. This class stores styles for characters, for example whether the character is bold, italic or underlined. But also the font-size and the font-family. So it has different types of member variables. The easiest way to implement this would be to add getters and setters for every member variable, but this just feels wrong to me. It feels way more logical (and more OOP) to call style.format(BOLD, true) instead of style.setBold(true). So to use logical methods insteads of getters/setters. But I am facing two problems while implementing these methods: I would need a big switch statement with all member variables, since you can't access a variable by the contents of a string in C++. Moreover, you can't overload by return type, which means you can't write one getter like style.getFormatting(BOLD) (I know there are some tricks to do this, but these don't allow for parameters, which I would obviously need). However, if I would implement getters and setters, there are also issues. I would have to duplicate quite some code because styles can also have a parent styles, which means the getters have to look not only at the member variables of this style, but also at the variables of the parent styles. Because I wasn't able to figure out how to do this, I decided to ask a question a couple of weeks ago. See Object Oriented Programming: getters/setters or logical names. But in that question I didn't stress it would be just a data object and that I'm not making a text rendering engine, which was the reason one of the people that answered suggested I ask another question while making that clear (because his solution, the decorator pattern, isn't suitable for my problem). So please note that I'm not creating my own text rendering engine, I just use these classes to store data. Because I still haven't been able to find a solution to this problem I'd like to ask this question again: how would you design a styles class like this? And why would you do that? Thanks on forehand!

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• How to REALLY start thinking in terms of objects?

  - by Mr Grieves

  I work with a team of developers who all have several years of experience with languages such as C# and Java. Most of them are young enough to have been shown OOP as a standard way to develop software in university and are very comfortable with concepts such as inheritance, abstraction, encapsulation and polymorphism. Yet, many of them, and I have to include myself, still tend to create classes which are meant to be used in a very functional fashion. The resulting software is often several smaller classes which correctly represent business objects which get passed through larger classes which only supply ways to modify and use those objects (functions). Large complex difficult-to-maintain classes named Manager are usually the result of such behaviour. I can see two theoretical reasons why people might write this type of code: It's easy to start thinking of everything in terms of the database Deep down, for me, a computer handling a web request feels more like a functional operation than an object oriented operation when you think about Request Handlers, Threads, Processes, CPU Cores and CPU operations... I want source code which is easy to read and easy to modify. I have seen excellent examples of OO code which meet these objectives. How can I start writing code like this? How I can I really start thinking in an object oriented fashion? How can I share such a mentality with my colleagues?

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• How to distinguish doc, ppt, xls files, without looking at file extension

  - by Shelby. S

  So I was wondering how would you differentiate ppt, xls and doc files from each other in linux regardless of extensions. I tried 'file' but from the looks of it, all of MSOffice files are categorized under the same file type. Similarly I'm having trouble with docx, xlsx and pptx files, since they're essentially all zip files containing a bunch of xml. I also tried a python script importing the magic module, but no go. I'm trying to identify the actual file for a sandbox analysis. And for this specific purpose I need to find the actual file type in order to run it in the sandbox vm (the Windows vm runs everything by extension). Let's say my sample file is labeled as try.exe, but in reality it's just a doc file. My script will rename it as try.exe.doc, which would work fine for doc files. But since linux identifies all MSOffice files as simple DOC files then there's no way to identify ppt or xls files. As a result the sandbox wont' analyze the sample correctly.

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• Matlab: Why is '1' + 1 == 50? [migrated]

  - by phi

  Matlab has weak dynamic typing, which is what causes this weird behaviour. What I do not understand is what exactly happens, as this result really surprises me. Edit: To clarify, what I'm describing is clearly a result of Matlab storing chars in ASCII-format, which was also mentioned in the comments. I'm more interested in the way Matlab handles its variables, and specifically, how and when it assigns a type/tag to the values. Thanks. '1' is a 1-by-1 matrix of chars in matlab and '123' is a 1-by-3 matrix of chars. As expected, 1 returns a 1-by-1 double. Now if I enter '1' + 1 I get 50 as a 1-by-1 double, and if I enter '123' + 1 I get a 1-by-3 double [ 50 51 52 ] Furthermore, if I type 'a' + 1 the result is 98 in a 1-by-1 double. I assume this has to do with how Matlab stores char-variables in ascii form, but how exactly is it handling these? Are the data actually unityped and tagged, or how does it work? Thanks.

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• How to implement isValid correctly?

  - by Songo

  I'm trying to provide a mechanism for validating my object like this: class SomeObject { private $_inputString; private $_errors=array(); public function __construct($inputString) { $this->_inputString = $inputString; } public function getErrors() { return $this->_errors; } public function isValid() { $isValid = preg_match("/Some regular expression here/", $this->_inputString); if($isValid==0){ $this->_errors[]= 'Error was found in the input'; } return $isValid==1; } } Then when I'm testing my code I'm doing it like this: $obj = new SomeObject('an INVALID input string'); $isValid = $obj->isValid(); $errors=$obj->getErrors(); $this->assertFalse($isValid); $this->assertNotEmpty($errors); Now the test passes correctly, but I noticed a design problem here. What if the user called $obj->getErrors() before calling $obj->isValid()? The test will fail because the user has to validate the object first before checking the error resulting from validation. I think this way the user depends on a sequence of action to work properly which I think is a bad thing because it exposes the internal behaviour of the class. How do I solve this problem? Should I tell the user explicitly to validate first? Where do I mention that? Should I change the way I validate? Is there a better solution for this? UPDATE: I'm still developing the class so changes are easy and renaming functions and refactoring them is possible.

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• OOP Design: relationship between entity classes

  - by beginner_

  I have at first sight a simple issue but can't wrap my head around on how to solve. I have an abstract class Compound. A Compound is made up of Structures. Then there is also a Container which holds 1 Compound. A "special" implementation of Compound has Versions. For that type of Compound I want the Container to hold the Versionof the Compound and not the Compound itself. You could say "just create an interface Containable" and a Container holds 1 Containable. However that won't work. The reason is I'm creating a framework and the main part of that framework is to simplify storing and especially searching for special data type held by Structure objects. Hence to search for Containers which contain a Compound made up of a specific Structure requires that the "Path" from Containerto Structure is well defined (Number of relationships or joins). I hope this was understandable. My question is how to design the classes and relationships to be able to do what I outlined.

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• Which order to define getters and setters in? [closed]

  - by N.N.

  Is there a best practice for the order to define getters and setters in? There seems to be two practices: getter/setter pairs first getters, then setters (or the other way around) To illuminate the difference here is a Java example of getter/setter pairs: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public void setVar1(int var1) { this.var1 = var1; } public int getVar2() { return var2; } public void setVar2(int var2) { this.var2 = var2; } public int getVar3() { return var3; } public void setVar3(int var3) { this.var3 = var3; } } And here is a Java example of first getters, then setters: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public int getVar2() { return var2; } public int getVar3() { return var3; } public void setVar1(int var1) { this.var1 = var1; } public void setVar2(int var2) { this.var2 = var2; } public void setVar3(int var3) { this.var3 = var3; } } I think the latter type of ordering is clearer both in code and in class diagrams but I do not know if that is enough to rule out the other type of ordering.

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• How can I make the C# compiler infer these type parameters automatically?

  - by John Feminella

  I have some code that looks like the following. First I have some domain classes and some special comparators for them. public class Fruit { public int Calories { get; set; } public string Name { get; set; } } public class FruitEqualityComparer : IEqualityComparer<Fruit> { // ... } public class BasketEqualityComparer : IEqualityComparer<IEnumerable<Fruit>> { // ... } Next, I have a helper class called ConstraintChecker. It has a simple BaseEquals method that makes sure some simple base cases are considered: public static class ConstraintChecker { public static bool BaseEquals(T lhs, T rhs) { bool sameObject = l == r; bool leftNull = l == null; bool rightNull = r == null; return sameObject && !leftNull && !rightNull; } There's also a SemanticEquals method which is just a BaseEquals check and a comparator function that you specify. public static bool SemanticEquals<T>(T lhs, T rhs, Func<T, T, bool> f) { return BaseEquals(lhs, rhs) && f(lhs, rhs); } And finally there's a SemanticSequenceEquals method which accepts two IEnumerable<T> instances to compare, and an IEqualityComparer instance that will get called on each pair of elements in the list via Enumerable.SequenceEquals. public static bool SemanticSequenceEquals<T, U, V>(U lhs, U rhs, V comparator) where U : IEnumerable<T> where V : IEqualityComparer<T> { return SemanticEquals(lhs, rhs, (l, r) => lhs.SequenceEqual(rhs, comparator)); } } // end of ConstraintChecker The point of SemanticSequenceEquals is that you don't have to define two comparators whenever you want to compare both IEnumerable<T> and T instances; now you can just specify an IEqualityComparer<T> and it will also handle lists when you invoke SemanticSequenceEquals. So I could get rid of the BasketEqualityComparer class, which would be nice. But there's a problem. The C# compiler can't figure out the types involved when you invoke SemanticSequenceEquals: return ConstraintChecker.SemanticSequenceEquals(lhs, rhs, new FruitEqualityComparer()); If I specify them explicitly, it works: return ConstraintChecker.SemanticSequenceEquals< Fruit, IEnumerable<Fruit>, IEqualityComparer<Fruit> > (lhs, rhs, new FruitEqualityComparer()); What can I change here so that I don't have to write the type parameters explicitly?

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• What's faster? select [object] or select new {[object].value1, [object].value2} with linq

  - by Darcy

  I was hoping some of you guru's out there know the answer to this question. Which is faster? A or B A: var item = from d in database select d; B: var item = from d in database select new {d.item1, d.item2}; SEEMINGLY, it seems like selecting part of the table object would be faster than selecting the entire object, but something tells me its not necessarily the case.

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• Why is my (Type).GetFields(BindingFlags.Instance | BindingFlags.Public) not working?

  - by granadaCoder

  My code can see the NonPublic members, but not the Public ones. (???) Full sample code below. FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); is returning nothing. Note, I'm trying to get at the properties on the abstract class as well as the 1 concrete class. (And read the attributes as well). I'm going bonkers on this one....the msdn example works with the 2 flags (BindingFlags.Instance | BindingFlags.Public).....but my mini inheritance example below is not. THANKS in advance. /////////////START CODE private void RunTest1() { try { textBox1.Text = string.Empty; Type t = typeof(MyInheritedClass); //Look at the BindingFlags *** NonPublic *** int fieldCount = 0; while (null != t) { fieldCount += t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic).Length; FieldInfo[] nonPublicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic); foreach (FieldInfo field in nonPublicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); } } t = t.BaseType; } Console.WriteLine("\n\r------------------\n\r"); //Look at the BindingFlags *** Public *** t = typeof(MyInheritedClass); FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); foreach (FieldInfo field in publicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); object[] attributes = field.GetCustomAttributes(t, true); if (attributes != null && attributes.Length > 0) { foreach (Attribute att in attributes) { Console.WriteLine(att.GetType().Name); } } } } } catch (Exception ex) { ReportException(ex); } } private void ReportException(Exception ex) { Exception innerException = ex; while (innerException != null) { Console.WriteLine(innerException.Message + System.Environment.NewLine + innerException.StackTrace + System.Environment.NewLine + System.Environment.NewLine); innerException = innerException.InnerException; } } public abstract class MySuperType { public MySuperType(string st) { this.STString = st; } public string STString { get; set; } public abstract string MyAbstractString {get;set;} } public class MyInheritedClass : MySuperType { public MyInheritedClass(string ic) : base(ic) { this.ICString = ic; } [Description("This is an important property"),Category("HowImportant")] public string ICString { get; set; } private string _oldSchoolPropertyString = string.Empty; public string OldSchoolPropertyString { get { return _oldSchoolPropertyString; } set { _oldSchoolPropertyString = value; } } [Description("This is a not so importarnt property"), Category("HowImportant")] public override string MyAbstractString { get; set; } }

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• SQL SERVER – Signal Wait Time Introduction with Simple Example – Wait Type – Day 2 of 28

  - by pinaldave

  In this post, let’s delve a bit more in depth regarding wait stats. The very first question: when do the wait stats occur? Here is the simple answer. When SQL Server is executing any task, and if for any reason it has to wait for resources to execute the task, this wait is recorded by SQL Server with the reason for the delay. Later on we can analyze these wait stats to understand the reason the task was delayed and maybe we can eliminate the wait for SQL Server. It is not always possible to remove the wait type 100%, but there are few suggestions that can help. Before we continue learning about wait types and wait stats, we need to understand three important milestones of the query life-cycle. Running - a query which is being executed on a CPU is called a running query. This query is responsible for CPU time. Runnable – a query which is ready to execute and waiting for its turn to run is called a runnable query. This query is responsible for Signal Wait time. (In other words, the query is ready to run but CPU is servicing another query). Suspended – a query which is waiting due to any reason (to know the reason, we are learning wait stats) to be converted to runnable is suspended query. This query is responsible for wait time. (In other words, this is the time we are trying to reduce). In simple words, query execution time is a summation of the query Executing CPU Time (Running) + Query Wait Time (Suspended) + Query Signal Wait Time (Runnable). Again, it may be possible a query goes to all these stats multiple times. Let us try to understand the whole thing with a simple analogy of a taxi and a passenger. Two friends, Tom and Danny, go to the mall together. When they leave the mall, they decide to take a taxi. Tom and Danny both stand in the line waiting for their turn to get into the taxi. This is the Signal Wait Time as they are ready to get into the taxi but the taxis are currently serving other customer and they have to wait for their turn. In other word they are in a runnable state. Now when it is their turn to get into the taxi, the taxi driver informs them he does not take credit cards and only cash is accepted. Neither Tom nor Danny have enough cash, they both cannot get into the vehicle. Tom waits outside in the queue and Danny goes to ATM to fetch the cash. During this time the taxi cannot wait, they have to let other passengers get into the taxi. As Tom and Danny both are outside in the queue, this is the Query Wait Time and they are in the suspended state. They cannot do anything till they get the cash. Once Danny gets the cash, they are both standing in the line again, creating one more Signal Wait Time. This time when their turn comes they can pay the taxi driver in cash and reach their destination. The time taken for the taxi to get from the mall to the destination is running time (CPU time) and the taxi is running. I hope this analogy is bit clear with the wait stats. You can check the Signalwait stats using following query of Glenn Berry. -- Signal Waits for instance SELECT CAST(100.0 * SUM(signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2)) AS [%signal (cpu) waits], CAST(100.0 * SUM(wait_time_ms - signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2)) AS [%resource waits] FROM sys.dm_os_wait_stats OPTION (RECOMPILE); Higher the Signal wait stats are not good for the system. Very high value indicates CPU pressure. In my experience, when systems are running smooth and without any glitch the Signal wait stat is lower than 20%. Again, this number can be debated (and it is from my experience and is not documented anywhere). In other words, lower is better and higher is not good for the system. In future articles we will discuss in detail the various wait types and wait stats and their resolution. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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