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• How can I set up an editor to work with Git on Windows?

  - by Patrick McElhaney

  I'm trying out Git on Windows. I got to the point of trying "git commit" and I got this error: Terminal is dumb but no VISUAL nor EDITOR defined. Please supply the message using either -m or -F option. So I figured out I need to have an environment variable called EDITOR. No problem. I set it to point to Notepad. That worked, almost. The default commit message opens in Notepad. But Notepad doesn't support bare line feeds. I went out and got Notepad++. But I can't figure out how to get Notepad++ set up as the %EDITOR% in such a way that it works with Git as expected. I'm not married to Notepad++. At this point I couldn't care less what editor I use. I just want to be able to type my commit messages without using -m. So, for those of you using Git on Windows: What (free) tool do you use to edit your commit message, and what do you get when you type echo %EDITOR% at the command prompt?

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• How to create instances of related models in Django

  - by sevennineteen

  I'm working on a CMSy app for which I've implemented a set of models which allow for creation of custom Template instances, made up of a number of Fields and tied to a specific Customer. The end-goal is that one or more templates with a set of custom fields can be defined through the Admin interface and associated to a customer, so that customer can then create content objects in the format prescribed by the template. I seem to have gotten this hooked up such that I can create any number of Template objects, but I'm struggling with how to create instances - actual content objects - in those templates. For example, I can define a template "Basic Page" for customer "Acme" which has the fields "Title" and "Body", but I haven't figured out how to create Basic Page instances where these fields can be filled in. Here are my (somewhat elided) models... class Customer(models.Model): ... class Field(models.Model): ... class Template(models.Model): label = models.CharField(max_length=255) clients = models.ManyToManyField(Customer, blank=True) fields = models.ManyToManyField(Field, blank=True) class ContentObject(models.Model): label = models.CharField(max_length=255) template = models.ForeignKey(Template) author = models.ForeignKey(User) customer = models.ForeignKey(Customer) mod_date = models.DateTimeField('Modified Date', editable=False) def __unicode__(self): return '%s (%s)' % (self.label, self.template) def save(self): self.mod_date = datetime.datetime.now() super(ContentObject, self).save() Thanks in advance for any advice!

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• How can I alter an external variable from inside my AJAX?

  - by tmedge

  I keep on having these same two problems. I have been trying to use Remy Sharp's wonderful tagSuggest plugin, and it works great. Until I try to use an AJAX call to get tags from my database. My setGlobalTags() works great, with my defined myTagList at the top of the function. What I want to do is set myTagList equal to the result from my AJAX. My problem is that I can neither call setGlobalTags() from inside my success or error functions, nor actually alter the original myTagList. Also, I keep on having this other issue as well. I keep this code in my Master page, and my AJAX returns 'success' on almost every page. I only (and always) get the error alert when I navigate to a page that actually contains something of id="ParentTags". I don't see why this is happening, because my $('#ParentTags').tagSuggest(); is definitely after my AJAX call. I realize that this is probably just some dumb conventions error, but I am new to this and I'm here to learn from you guys. Thanks in advance! $(function() { var myTagList = ['test', 'testMore', 'testALot']; $.ajax({ type: "POST", url: 'Admin/GetTagList', dataType: 'json', success: function(resultTags) { myTagList = resultTags; alert(myTagList[0]); setGlobalTags(myTagList); }, error: function() { alert('Error'); setGlobalTags(myTagList); } }); setGlobalTags(myTagList); $('#ParentTags').tagSuggest(); });

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• Java many to many association map

  - by Raphael Jolivet

  Hi, I have to classes, ClassA and ClassB and a "many to many" AssociationClass. I want to use a structure to hold the associations between A and B such as I can know, for each instance of A or B, which are their counterparts. I thought of using a Hashmap, with pair keys: Hasmap<Pair<ClassA, ClassB>, AssociationClass> associations; This way, I can add and remove an association between two instances of ClassA and ClassB, and I can query a relation for two given instances. However, I miss the feature of getting all associations defined for a given instance of ClassA or ClassB. I could do it by brute force and loop over all keys of the map to search for associations between a given instance, but this is inefficient and not elegant. Do you know of any data structure / free library that enables this ? I don't want to reinvent the wheel. Thanks in advance for your help, Raphael NB: This is not a "database" question. These objects are pure POJO used for live computation, I don't need persistence stuff.

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• ExternalInterface issue on loadup with FireFox

  - by Rudy

  Hello, I have an issue with my ExternalInterface. The way it is currently set up is, on the page load up, a boolean is set to true in JavaScript and then checked by ActionScript constructors (using a timer) until it is true. This marks that JavaScript is ready to get calls from AS3. At this point, AS3 will add the callback and do some internal stuff, and at the end of the constructor I call JavaScript. So far so good. JavaScript will at this point call a function in AS3 (that was defined in the callback described above), and this is where it all messes up. On IE this works perfectly fine. On FireFox though, it does not. When I debug it, I see that the javascript function is called but when it tries to call AS3, nothing happens. I also tried to add a timer, but for some reason the function STILL executes straight away (in IE). What is very weird is that a second or two later, that function will work, so it seems that the Flash is not completely loaded in FireFox? But it runs to the last line of my constructor, so I would believe it's loaded. Any idea please, I am really stuck. Thanks a lot, Rudy

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• What MS technology to use for HTTP service returning XML?

  - by Borek

  I need to create a service that: accepts HTTP requests (with query string or HTTP POST parameters) does some processing on the requests (checking if the request is valid, authentication etc.) reads data from a custom store (another HTTP call in our case) returns the result as custom XML (defined with XSD) I'm trying to think of various MS technologies that could help me and how good they would be for this scenario (pretty standard one I guess). The tasks above are relatively separate, this is what comes to mind: HTTP front-end: ASP.NET Web Forms ASP.NET MVC (seems more appropriate here as I won't need server controls, view state etc.) WCF? Don't know much about it or how well it would suit my task. Custom logic on the server: this will probably be a generic C# code in all cases (sometimes "plugged into" or called from MVC controllers or some equivalent place in other technologies) Reading data from internal data stores: As said, this is another HTTP server in our case. Options that come to mind: Just read the data using something like WebClient (Just theoretically) implement a LINQ provider (Just even more theoretically) implement an EF provider Output the data as custom XML: Linq2XML Serialization? Is it flexible enough? Does WCF provide some tools for this? Some "OXM" - Object/XML mapper if there is something like that for .NET I may be wrong in many of my assumptions, this is just a quick list that comes to mind after a quick research. Some general notes / questions: Testing is important Solution with a clear domain model would be much preferred over the one without Can Entity Framework actually help somewhere in my scenario? If so, where and how? Would WCF be an appropriate technology for this? I don't know much about it.

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• How to test for existence of a script-scoped variable in PowerShell?

  - by Damian Powell

  Is it possible to test for the existence of a script-scoped variable in PowerShell? I've been using the PowerShell Community Extensions (PSCX) but I've noticed that if you import the module while Set-PSDebug -Strict is set, an error is produced: The variable '$SCRIPT:helpCache' cannot be retrieved because it has not been set. At C:\Users\...\Modules\Pscx\Modules\GetHelp\Pscx.GetHelp.psm1:5 char:24 While investigating how I might fix this, I found this piece of code in Pscx.GetHelp.psm1: #requires -version 2.0 param([string[]]$PreCacheList) if ((!$SCRIPT:helpCache) -or $RefreshCache) { $SCRIPT:helpCache = @{} } This is pretty straight forward code; if the cache doesn't exist or needs to be refreshed, create a new, empty cache. The problem is that calling $SCRIPT:helpCache while Set-PSDebug -Strict is in force casues the error because the variable hasn't been defined yet. Ideally, we could use a Test-Variable cmdlet but such a thing doesn't exist! I thought about looking in the variable: provider but I don't know how to determine the scope of a variable. So my question is: how can I test for the existence of a variable while Set-PSDebug -Strict is in force, without causing an error?

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• Domain model: should things like Logging, Audit, Persistence be in it

  - by hom.tanks

  I'm having a hard time convincing our architect that a Domain model should only have the essential elements of the business domain on it. Things like the fact that a class is persistable, that it needs logging and auditing and that it has a RESTful URI should not drive the domain model. They can be added later on, by using interfaces. Ours is a healthcare information management system. At the very coarse level, its a system where users login and access their healthcare information. They can share this information with others and be custodian for others' information (think Roles). But because of a few sound bytes that caught on early like "Everything should be a REST resource" the model now has a top level class called Resource that every other class extends from. I'm trying to make him see that the domain model should have well defined concepts like User Account, HealthDocument, UserRole etc which are distinct entities of the business , with specific associations between them. Clubbing everything under Resource class lets our model be inflexible besides being potentially incorrect. But he wants me to show him why its a bad idea to do it his way. I don't know how to articulate that properly but all my OO instincts tell me that its just not right. Any thoughts?

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• g++ linker can't find const member function

  - by Max

  I have a Point class (with integer members x and y) that has a member function withinBounds that is declared like so: bool withinBounds(const Point&, const Point&) const; and defined like this: bool Point::withinBounds(const Point& TL, const Point& BR) const { if(x < TL.getX()) return false; if(x > BR.getX()) return false; if(y < TL.getY()) return false; if(y > BR.getY()) return false; // Success return true; } and then in another file, I call withinBounds like this: Point pos = currentPlayer->getPosition(); if(pos.withinBounds(topleft, bottomright)) { // code block } This compiles fine, but it fails to link. g++ gives me this error: /home/max/Desktop/Development/YARL/yarl/src/GameData.cpp:61: undefined reference to 'yarl::utility::Point::withinBounds(yarl::utility::Point const&, yarl::utility::Point const&)' When I make the function not const, it links fine. Anyone know the reason why? The linker error looks like it's looking for a non-const version of the function, but I don't know why it would.

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• C# parameters by reference and .net garbage collection

  - by Yarko

  I have been trying to figure out the intricacies of the .NET garbage collection system and I have a question related to C# reference parameters. If I understand correctly, variables defined in a method are stored on the stack and are not affected by garbage collection. So, in this example: public class Test { public Test() { } public int DoIt() { int t = 7; Increment(ref t); return t; } private int Increment(ref int p) { p++; } } the return value of DoIt() will be 8. Since the location of t is on the stack, then that memory cannot be garbage collected or compacted and the reference variable in Increment() will always point to the proper contents of t. However, suppose we have: public class Test { private int t = 7; public Test() { } public int DoIt() { Increment(ref t); return t; } private int Increment(ref int p) { p++; } } Now, t is stored on the heap as it is a value of a specific instance of my class. Isn't this possibly a problem if I pass this value as a reference parameter? If I pass t as a reference parameter, p will point to the current location of t. However, if the garbage collector moves this object during a compact, won't that mess up the reference to t in Increment()? Or does the garbage collector update even references created by passing reference parameters? Do I have to worry about this at all? The only mention of worrying about memory being compacted on MSDN (that I can find) is in relation to passing managed references to unmanaged code. Hopefully that's because I don't have to worry about any managed references in managed code. :)

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• What is the performance penalty of XML data type in SQL Server when compared to NVARCHAR(MAX)?

  - by Piotr Owsiak

  I have a DB that is going to keep log entries. One of the columns in the log table contains serialized (to XML) objects and a guy on my team proposed to go with XML data type rather than NVARCHAR(MAX). This table will have logs kept "forever" (archiving some very old entries may be considered in the future). I'm a little worried about the CPU overhead, but I'm even more worried that DB can grow faster (FoxyBOA from the referenced question got 70% bigger DB when using XML). I have read this question http://stackoverflow.com/questions/514827/microsoft-sql-server-2005-2008-xml-vs-text-varchar-data-type and it gave me some ideas but I am particulairly interrested in clarification on whether the DB size increases or decreases. Can you please share your insight/experiences in that matter. BTW. I don't currently have any need to depend on XML features within SQL Server (there's nearly zero advantage to me in the specific case). Ocasionally log entries will be extracted, but I prefer to handle the XML using .NET (either by writing a small client or using a function defined in a .NET assembly).

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• Extension methods for encapsulation and reusability

  - by tzaman

  In C++ programming, it's generally considered good practice to "prefer non-member non-friend functions" instead of instance methods. This has been recommended by Scott Meyers in this classic Dr. Dobbs article, and repeated by Herb Sutter and Andrei Alexandrescu in C++ Coding Standards (item 44); the general argument being that if a function can do its job solely by relying on the public interface exposed by the class, it actually increases encapsulation to have it be external. While this confuses the "packaging" of the class to some extent, the benefits are generally considered worth it. Now, ever since I've started programming in C#, I've had a feeling that here is the ultimate expression of the concept that they're trying to achieve with "non-member, non-friend functions that are part of a class interface". C# adds two crucial components to the mix - the first being interfaces, and the second extension methods: Interfaces allow a class to formally specify their public contract, the methods and properties that they're exposing to the world. Any other class can choose to implement the same interface and fulfill that same contract. Extension methods can be defined on an interface, providing any functionality that can be implemented via the interface to all implementers automatically. And best of all, because of the "instance syntax" sugar and IDE support, they can be called the same way as any other instance method, eliminating the cognitive overhead! So you get the encapsulation benefits of "non-member, non-friend" functions with the convenience of members. Seems like the best of both worlds to me; the .NET library itself providing a shining example in LINQ. However, everywhere I look I see people warning against extension method overuse; even the MSDN page itself states: In general, we recommend that you implement extension methods sparingly and only when you have to. So what's the verdict? Are extension methods the acme of encapsulation and code reuse, or am I just deluding myself?

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• What happened to the .NET version definition with v4.0?

  - by Tom Tresansky

  I'm building a C# class library, and using the beta 2 of Visual Web Developer/Visual C# 2010. I'm trying to save information about what version of .NET the library was built under. In the past, I was able to use this: // What version of .net was it built under? #if NET_1_0 public const string NETFrameworkVersion = ".NET 1.0"; #elif NET_1_1 public const string NETFrameworkVersion = ".NET 1.1"; #elif NET_2_0 public const string NETFrameworkVersion = ".NET 2.0"; #elif NET_3_5 public const string NETFrameworkVersion = ".NET 3.5"; #else public const string NETFrameworkVersion = ".NET version unknown"; #endif So I figured I could just add: #elif NET_4_0 public const string NETFrameworkVersion = ".NET 4.0"; Now, in Project-Properties, my target Framework is ".NET Framework 4". If I check: Assembly.GetExecutingAssembly().ImageRuntimeVersion I can see my runtime version is v4.0.21006 (so I know I have .NET 4.0 installed on my CPU). I naturally expect to see that my NETFrameworkVersion variable holds ".NET 4.0". It does not. It holds ".NET version unknown". So my question is, why is NET_4_0 not defined? Did the naming convention change? Is there some simple other way to determine .NET framework build version in versions 3.5?

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• How to use IsKeyboardFocusWithin and IsSelected together?

  - by jpsstavares

  I have a style defined for my ListBoxItems with a trigger to set a background color when IsSelected is True: <Style x:Key="StepItemStyle" TargetType="{x:Type ListBoxItem}"> <Setter Property="SnapsToDevicePixels" Value="true"/> <Setter Property="OverridesDefaultStyle" Value="true"/> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="ListBoxItem"> <Border Name="Border" Padding="0" SnapsToDevicePixels="true"> <ContentPresenter /> </Border> <ControlTemplate.Triggers> <Trigger Property="IsSelected" Value="True"> <Setter TargetName="Border" Property="Background" Value="#40a0f5ff"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> </Setter.Value> </Setter> </Style> This style maintains the selected item even when the ListBox and ListBoxItem loses focus, which in my case is an absolute must. The problem is that I also want the ListBoxItem to be selected when one of its TextBox's child gets focused. To achieve this I add a trigger that sets IsSelected to true when IsKeyboardFocusWithin is true: <Trigger Property="IsKeyboardFocusWithin" Value="True"> <Setter Property="IsSelected" Value="True" /> </Trigger> When I add this trigger the Item is selected when the focus is on a child TextBox, but the first behaviour disappears. Now when I click outside the ListBox, the item is de-selected. How can I keep both behaviours?

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• Which to use, XMP or RDF?

  - by zotty

  What's the difference between RDF and XMP? From what I can tell, XMP is derived from RDF... so what does it offer that RDF doesn't? My particular situation is this: I've got some images which need tagging with details of how an experiment was performed, and what sort of data analysis has been performed on the images. A colleague of mine is pushing for XMP, but he's thinking of the images as photos - they're not really, they're just bits of data. From what I've seen (mainly by opening images in notepad++) the XMP data looks very similar to RDF - even so far as using RDF in the tag names (e.g. <rdf:Seq>). I'd like this data to be usable by other people who use similar instruments for similar experiments, so creating a mini standard (schema?) seems like the way to go. Apologies for the lack of fundemental understanding - I'm a Doctor, not a programmer! If it makes any difference, the language of choice will be C#. Edit for more information: First off, thanks for the excellent replies - thinking of XMP as a vocabulary for RDF makes things a lot clearer. The sort of data I'll be storing wont be avaliable in any of the pre-defined sets. It'll detail experimental set ups, locations and results. I think using RDF is the way to go.

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• JSP: How can I still get the code on my error page to run, even if I can't display it?

  - by Josh Hinman

  I've defined an error-page in my web.xml: <error-page> <exception-type>java.lang.Exception</exception-type> <location>/error.jsp</location> </error-page> In that error page, I have a custom tag that I created. The tag handler for this tag e-mails me the stacktrace of whatever error occurred. For the most part this works great. Where it doesn't work great is if the output has already begun being sent to the client at the time the error occurs. In that case, we get this: SEVERE: Exception Processing ErrorPage[exceptionType=java.lang.Exception, location=/error.jsp] java.lang.IllegalStateException I believe this error happens because we can't redirect a request to the error page after output has already started. The work-around I've used is to increase the buffer size on particularly large JSP pages. But I'm trying to write a generic error handler that I can apply to existing applications, and I'm not sure it's feasible to go through hundreds of JSP pages making sure their buffers are big enough. Is there a way to still allow my stack trace e-mail code to execute in this case, even if I can't actually display the error page to the client?

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• Execute function without sending 'self' to it

  - by Sergey

  Is that possible to define a function without referencing to self this way? def myfunc(var_a,var_b) But so that it could also get sender data, like if I defined it like this: def myfunc(self, var_a,var_b) That self is always the same so it looks a little redundant here always to run a function this way: myfunc(self,'data_a','data_b'). Then I would like to get its data in the function like this sender.fields. UPDATE: Here is some code to understand better what I mean. The class below is used to show a page based on Jinja2 templates engine for users to sign up. class SignupHandler(webapp.RequestHandler): def get(self, *args, **kwargs): utils.render_template(self, 'signup.html') And this code below is a render_template that I created as wrapper to Jinja2 functions to use it more conveniently in my project: def render_template(response, template_name, vars=dict(), is_string=False): template_dirs = [os.path.join(root(), 'templates')] logging.info(template_dirs[0]) env = Environment(loader=FileSystemLoader(template_dirs)) try: template = env.get_template(template_name) except TemplateNotFound: raise TemplateNotFound(template_name) content = template.render(vars) if is_string: return content else: response.response.out.write(content) As I use this function render_template very often in my project and usually the same way, just with different template files, I wondered if there was a way to get rid of having to call it like I do it now, with self as the first argument but still having access to that object.

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• Delphi Client-Server Application using Firebird 2.5 embedded connection error

  - by Japster

  0 down vote favorite 1 share [fb] share [tw] I have got a lengthy question to ask. First of all Im still very new when it comes to Delphi programming and my experience has beem mostly developing small single user database applications using ADO and an Access database. I need to take the transition now to a client server application and this is where the problem starts. I decided to use Firebird 2.5 embeded as my database, as it is open source, and it is can be used with the interbase components in Delphi and that multiple clients can access the database simultanously. So I followed the interbase tutorial in Delphi. I managed to connect the client to the server and see the data in the example (While both are running on my pc), but when i tried to move the client to another pc, keeping the server on mine and running it to see if I can connect to the server it gave me the following error. Exception EIdSocketError in module clientDemo.exe at 0029DCAC. Socket Error # 10061 Connection refused. I understand that this might be because the host is defined as localhost in the client. But here is my first question. In the TSQLConncetion you can set die hostname under Driver-Hostname. The thing I want to know is how do you do this at run time, as I cannot get the property when I try and make an edit box to allow the user to enter the value and then set it via code like for example: SQLConncetion1.Driver.Hostname := edtHost.text; This cannot be done this way and the only way I see you can set the hostname is with the object inspector, but that is not available at runtime and I need to set the hostname on the client when the program is running the first time, so how do you set the hostname/IP address at runtime? Im using Delphi XE2 There is still a lot of questions to come especially when it comes to deployment, but I will take this piece by piece and I appreciate the advice.

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• How do I use IPTC/EXIF metadata to categorise photos?

  - by kbro

  Many photo viewing and editing applications allow you to examine and change EXIF and IPTC data in JPEG and other image files. For example, I can see things like shutter speed, aperture and orientation in the picture files that come off my Canon A430. There are many, many name/value pairs in all this metadata. But... What do I do if I want to store some data that doesn't have a build-in field name. Let's say I'm photographing an athletics competition and I want to tag every photo with the competitor's bib number. Can I create a "bib_number" field and assign it a values of "0001", "5478", "8124" etc, and then search for all photos with bib_number="5478"? I've spent a few hours searching and the best I can come up with is to put this custom information in the "keywords" field but this isn't quite what I'm after. With this socution I'd have to craft a query like "keywords contains bib_number_5478" whereas what I want it "bib_number is 5478". So do the EXIF and/or IPTC standards allow addtional user-defined field names? Thanks Kev

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• Dynamically added JTable not displaying

  - by Graza

  Java Newbie here. I have a JFrame that I added to my netbeans project, and I've added the following method to it, which creates a JTable. Problem is, for some reason when I call this method, the JTable isn't displayed. Any suggestions? public void showFromVectors(Vector colNames, Vector data) { jt = new javax.swing.JTable(data, colNames); sp = new javax.swing.JScrollPane(jt); //NB: "this" refers to my class DBGridForm, which extends JFrame this.add(sp,java.awt.BorderLayout.CENTER); this.setSize(640,480); } The method is called in the following context: DBGridForm gf = new DBGridForm(); //DBGridForm extends JFrame DBReader.outMatchesTable(gf); gf.setVisible(true); ... where DBReader.outMatchesTable() is defined as static public void outMatchesTable(DBGridForm gf) { DBReader ddb = new DBReader(); ddb.readMatchesTable(null); gf.showFromVectors(ddb.lastRsltColNames, ddb.lastRsltData); } My guess is I'm overlooking something, either about the swing classes I'm using, or about Java. Any ideas?

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• Does Perl auto-vivify variables used as references in subroutine calls?

  - by FM

  I've declared 2010 to be the year of higher-order programming, so I'm learning Haskell. The introduction has a slick quick-sort demo, and I thought, "Hey, that's easy to do in Perl". It turned to be easier than I expected. Note that I don't have to worry about whether my partitions ($less and $more) are defined. Normally you can't use an undefined value as an array reference. use strict; use warnings; use List::MoreUtils qw(part); my @data = (5,6,7,4,2,9,10,9,5,1); my @sorted = qsort(@data); print "@sorted\n"; sub qsort { return unless @_; my $pivot = shift @_; my ($less, $more) = part { $_ < $pivot ? 0 : 1 } @_; # Works, even though $less and $more are sometimes undefined. return qsort(@$less), $pivot, qsort(@$more); } As best I can tell, Perl will auto-vivify a variable that you try to use as a reference -- but only if you are passing it to a subroutine. For example, my call to foo() works, but not the attempted print. use Data::Dumper qw(Dumper); sub foo { print "Running foo(@_)\n" } my ($x); print Dumper($x); # Fatal: Can't use an undefined value as an ARRAY reference. # print @$x, "\n"; # But this works. foo(@$x); # Auto-vivification: $x is now []. print Dumper($x); My questions: Am I understanding this behavior correctly? What is the explanation or reasoning behind why Perl does this? Is this behavior explained anywhere in the docs?

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• Handle order dependence in loops

  - by Matt

  Hey all, I'm making a templating system where I instantiate each tag using a foreach loop. The issue is that some of the tags rely on each other so, I'm wondering how to get around that ordering from the looping. Here's an example: Class A { public $width; __construct() { $this->width = $B->width; // Undefined! Or atleast not set yet.. } } Class B { public $width; __construct() { $this->width = "500px"; } __tostring() { return "Hello World!"; } } Template.php $tags = array("A", "B"); foreach ($tags as $tag) { $TagObj[$tag] = new $tag(); } echo $TagObj['A']->width; // Nadamundo! EDIT: Ok just to clarify.. My main problem is that Class A relies on Class B, but class A is instantiated before class B, so therefore width has not yet been defined in class B. I am looking for a good way to make sure all the classes are loaded for everyone allowing the interdependencies to exist. For the future, please don't consider any syntax errors.. I just made up this example on the spot. Also assume that I have access to class B from class A after class B gets instantiated. I know this has applications elsewhere and I'm sure this has been solved before, if someone could enlighten me or point me in the right direction that'd be great! Thanks! Matt Mueler

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• C++ Multiple inheritance with interfaces?

  - by umanga

  Greetings all, I come from Java background and I am having difficulty with multiple inheritance. I have an interface called IView which has init() method.I want to derive a new class called PlaneViewer implementing above interface and extend another class. (QWidget). My implementation is as: IViwer.h (only Header file , no CPP file) : #ifndef IVIEWER_H_ #define IVIEWER_H_ class IViewer { public: //IViewer(); ///virtual //~IViewer(); virtual void init()=0; }; #endif /* IVIEWER_H_ */ My derived class. PlaneViewer.h #ifndef PLANEVIEWER_H #define PLANEVIEWER_H #include <QtGui/QWidget> #include "ui_planeviewer.h" #include "IViewer.h" class PlaneViewer : public QWidget , public IViewer { Q_OBJECT public: PlaneViewer(QWidget *parent = 0); ~PlaneViewer(); void init(); //do I have to define here also ? private: Ui::PlaneViewerClass ui; }; #endif // PLANEVIEWER_H PlaneViewer.cpp #include "planeviewer.h" PlaneViewer::PlaneViewer(QWidget *parent) : QWidget(parent) { ui.setupUi(this); } PlaneViewer::~PlaneViewer() { } void PlaneViewer::init(){ } My questions are: Is it necessary to declare method init() in PlaneViewer interface also , because it is already defined in IView? 2.I cannot complie above code ,give error : PlaneViewer]+0x28): undefined reference to `typeinfo for IViewer' collect2: ld returned 1 exit status Do I have to have implementation for IView in CPP file?

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• Zipping with padding in Haskell

  - by Travis Brown

  A couple of times I've found myself wanting a zip in Haskell that adds padding to the shorter list instead of truncating the longer one. This is easy enough to write. (Monoid works for me here, but you could also just pass in the elements that you want to use for padding.) zipPad :: (Monoid a, Monoid b) => [a] -> [b] -> [(a, b)] zipPad xs [] = zip xs (repeat mempty) zipPad [] ys = zip (repeat mempty) ys zipPad (x:xs) (y:ys) = (x, y) : zipPad xs ys This approach gets ugly when trying to define zipPad3. I typed up the following and then realized that of course it doesn't work: zipPad3 :: (Monoid a, Monoid b, Monoid c) => [a] -> [b] -> [c] -> [(a, b, c)] zipPad3 xs [] [] = zip3 xs (repeat mempty) (repeat mempty) zipPad3 [] ys [] = zip3 (repeat mempty) ys (repeat mempty) zipPad3 [] [] zs = zip3 (repeat mempty) (repeat mempty) zs zipPad3 xs ys [] = zip3 xs ys (repeat mempty) zipPad3 xs [] zs = zip3 xs (repeat mempty) zs zipPad3 [] ys zs = zip3 (repeat mempty) ys zs zipPad3 (x:xs) (y:ys) (z:zs) = (x, y, z) : zipPad3 xs ys zs At this point I cheated and just used length to pick the longest list and pad the others. Am I overlooking a more elegant way to do this, or is something like zipPad3 already defined somewhere?

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• C#/LINQ: How to define generically a keySelector for a templated class before calling OrderBy

  - by PierrOz

  Hi Folks, I have the following class defined in C# class myClass<T,U> { public T PropertyOne { get; set; } public U PropertyTwo { get; set; } } I need to write a function that reorder a list of myClass objects and takes two other parameters which define how I do this reorder: does my reordering depend on PropertyOne or PropertyTwo and is it ascending or descending. Let's say this two parameters are boolean. With my current knowledge in LINQ, I would write: public IList<myClass<T,U>> ReOrder(IList<myClass<T,U>> myList, bool usePropertyOne, bool ascending) { if (usePropertyOne) { if (ascending) { return myList.OrderBy(o => o.PropertyOne).ToList(); } else { return myList.OrderByDescending(o => o.PropertyOne).ToList(); } } else { if (ascending) { return myList.OrderBy(o => o.PropertyTwo).ToList(); } else { return myList.OrderByDescending(o => o.PropertyTwo).ToList(); } } } What could be a more efficient/elegant way to do that ? How can I declare the Func,TResult keySelector object to reuse when I call either OrderBy or OrderByDescending? I'm interesting in the answer since in my real life, I can have more than two properties.

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