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• Using C# and gppg, how would I construct an abstract syntax tree?

  - by Rupert

  Is there a way to do this almost out-of-the-box? I could go and write a big method that would use the collected tokens to figure out which leaves should be put in which branches and in the end populate a TreeNode object, but since gppg already handled everything by using supplied regular expressions, I was wondering if there's an easier way? Even if not, any pointers as to how best to approach the problem of creating an AST would be appreciated. Apologies if I said anything silly, I'm only just beginning to play the compiler game. :)

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• Is it considered bad form to execute a function within a conditional statement?

  - by michael

  Consider a situation in which you need to call successive routines and stop as soon as one returns a value that could be evaluated as positive (true, object, 1, str(1)). It's very tempting to do this: if (fruit = getOrange()) elseif (fruit = getApple()) elseif (fruit = getMango()) else fruit = new Banana(); return fruit; I like it, but this isn't a very recurrent style in what can be considered professional production code. One is likely to rather see more elaborate code like: fruit = getOrange(); if(!fruit){ fruit = getApple(); if(!fruit){ fruit = getMango(); if(!fruit){ fruit = new Banana(); } } } return fruit; According to the dogma on basic structures, is the previous form acceptable? Would you recommend it?

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• MS Access 2003 - Formatting results in a list box problem.

  - by Justin

  So I have a list box that displays averages in a table like format from a crossyab query. It's just what I need the query is right, there is just one thing. I had to set the field properties in the query as format: standard..decimal:2. Which is exactly what I needed. However..the list box will not pick up on this. First I typed the crosstab sql into the list box's properties....and then I ran into this problem. So then I actually just created the query object, saved it and set that as the rowsource for the list box. Still won't work....when I open the query it is the correct format. So is there a way to further format a text box? Is there a way tell it to limit decimal places to one or two on returned values? Thanks!

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• OO design for business logic

  - by hotyi

  I have one Sell Operation object and two Buy Operation objects, i want to implement such behavior that one Sell Operation discharges two Buy Operation, it looks like: sellOperation.Discharge(oneBuyOperation); sellOperation.Discharge(twoBuyOperation); so i want to ask whether i should call the repository function in the Discharge method, or i'd better call the repository save method outside Discharge method. like: opRepository.Save(sellOpertion); So anyone could give me some advise what are you going to implement in this scenario? using Service class or anything better way?

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• Why is django admin not accepting Nullable foreign keys?

  - by p.g.l.hall

  Here is a simplified version of one of my models: class ImportRule(models.Model): feed = models.ForeignKey(Feed) name = models.CharField(max_length=255) feed_provider_category = models.ForeignKey(FeedProviderCategory, null=True) target_subcategories = models.ManyToManyField(Subcategory) This class manages a rule for importing a list of items from a feed into the database. The admin system won't let me add an ImportRule without selecting a feed_provider_category despite it being declared in the model as nullable. The database (SQLite at the moment) even checks out ok: >>> .schema ... CREATE TABLE "someapp_importrule" ( "id" integer NOT NULL PRIMARY KEY, "feed_id" integer NOT NULL REFERENCES "someapp_feed" ("id"), "name" varchar(255) NOT NULL, "feed_provider_category_id" integer REFERENCES "someapp_feedprovidercategory" ("id"), ); ... I can create the object in the python shell easily enough: f = Feed.objects.get(pk=1) i = ImportRule(name='test', feed=f) i.save() ...but the admin system won't let me edit it, of course. How can I get the admin to let me edit/create objects without specifying that foreign key?

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• Setting a property value on each of the results in a FetchedResults set

  - by RickiG

  Hi On my Core Data Entity "Book" i have a boolean property, 'wasViewed' (NSNumber numberWithBool) that tells me if the Book was "viewed". I would like to implement a sort of "reset" this property for all my NSManagedObjects "Book". So that I can set them all to NO between sessions. I use an NSPredicate to retrieve all the Books like this: NSPredicate *predicate = [NSPredicate predicateWithFormat:@"wasViewed == %@", [NSNumber numberWithBool:YES]]; // code for setting entity, request etc... NSMutableArray *mutableFetchResults = [[[managedObjectContext executeFetchRequest:request error:&error] mutableCopy] autorelease]; This is working just fine, however, now I need to set up a loop, go through each Book object, something like this: for(Book *b in mutableFetchResults) { [b setWasViewed:NO] } Is there a way to perform an action on each element that fits the predicate instead of retrieving it? So instead of executeFetchRequest on a managedObjectContext it could be executeOperationOnFetchRequestResults or something along those lines. Thanks for any input given:)

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• Is there a limit on the number of mutex objects that can be created in a Windows process?

  - by young-phillip

  I'm writing a c# application that can create a series of request messages. Each message could have a response, that needs to be waited on by a consumer. Where the number of outstanding request messages is constrained, I have used the windows EVENT to solve this problem. However, I know there is a limit on how many EVENT objects can be created in a single process, and in this instance, its possible I might exceed that limit. Does anyone know if there is a similar limit on creation of mutex objects or semaphores? I know this can be solved by some sort of pool of shared resources, that are grabbed by consumers when they need to wait, but it would be more convenient if each request message could have its own sync object.

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• Ruby class instance variables and inheritance

  - by rlandster

  I have a Ruby class called LibraryItem. I want to associate with every instance of this class an array of attributes. This array is long and looks something like ['title', 'authors', 'location', ...] Note that these attributes are not really supposed to be methods, just a list of attributes that a LibraryItem has. Next, I want to make a subclass of LibraryItem called LibraryBook that has an array of attributes that includes all the attributes of LibraryItem but will also include many more. Eventually I will want several subclasses of LibraryItem each with their own version of the array @attributes but each adding on to LibraryItem's @attributes (e.g., LibraryBook, LibraryDVD, LibraryMap, etc.). So, here is my attempt: class LibraryItem < Object class << self; attr_accessor :attributes; end @attributes = ['title', 'authors', 'location',] end class LibraryBook < LibraryItem @attributes.push('ISBN', 'pages'] end This does not work. I get the error undefined method `push' for nil:NilClass

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• Accessing PostGIS spatial data from Rails

  - by Lakitu

  I need to use an existing PostGIS database from my Rails application. So far I am able to access the DB just fine, GeoRuby nicely converts the 'geom' column into a Point object. What I am looking for is an easy way to execute ActiveRecord-like queries on those tables, e.g. Poi.find_within_radius(...) or similar spatial queries like distance calculations et. al. I tried several combinations of geokit, accompanying rails plugins but I'm quite sure there must be something better out there in the ruby/rails universe. Any hints?

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• asp.net databinding string is passed to function but runtime occurs

  - by rod

  Hi All, I'm using a code-behind function (called TestFx) in my binding expression. I'm passing a string and the function accepts a string but I still get a runtime error saying invalid args. But if I change the method to accept an object and inspect the value, "it's a string!" Can someone please explain? -rod ProductDescription: <asp:Label ID="ProductDescriptionLabel" runat="server" Text='<%# TestFx(Eval("ProductDescription")) %>' /> <br />

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• how to register a selectionProvider for the Viewer from a superclass

  - by Tom

  I have a View which extends a View provided by another plugin like this; public class View2 extends some.other.package.View1 { public void createPartControl(Composite parent) { super.createPartControl(parent); //I want to do this, but I can't because its private //getSite().setSelectionProvider(treeViewer); } } But I can't edit the super class, so I need to access the viewer from the Control. public class some.other.package.View1 extends ViewPart { private TreeViewer treeViewer; public void createPartControl(Composite parent) { treeViewer = new TreeViewer(parent, SWT.V_SCROLL); } } I tried using parent.getChildren(); to get a Tree object, but I can't see that it can be cooerced into an ISElectionProvider as required

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• Problem with lazy loading implementation

  - by Mehran

  Hi, I have implemented lazy loading in my program. it's done through a proxy class like: class Order { public virtual IList<Item> Items {get; set;} } class OrderProxy { public override IList<Item> Items { get { if (base.Items == null) Items = GetItems(base.OrderID); return base.Items; } set { base.Items = value; } } } the problem is that whenever i instantiate proxy class,without even touching the Items property, it tries to load Items! as you may know,i want to instantiate proxy class and return the instance to BLL instead of domain object itself. what's the problem? Does .NET CLR access(read) properties in a class, when it's instatiating the class? any other methods? Thanks

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• How to determine Jet database Engine Type programmatically

  - by MZB

  I have a program which needs to upgrade any Access (Jet) database it opens to JET Version4.x if it isn't already that version. (This enables use of SQL-92 syntax features) Upgrading is (relatively) easy. A call to the JRO.JetEngine object's CompactDatabase method (as described here) should do the trick, but before I do this I need to determine whether an upgrade is required. How do I determine the Jet OLEDB:Engine Type of an existing database? Can this be determined from an open OleDBConnection? Note: I'm talking about database versions, not Jet library versions. C# or .Net solution greatly appreciated.

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• Scala and the Java Memory Model

  - by Ben Lings

  The Java Memory Model (since 1.5) treats final fields differently to non-final fields. In particular, provided the this reference doesn't escape during construction, writes to final fields in the constructor are guaranteed to be visible on other threads even if the object is made available to the other thread via a data race. (Writes to non-final fields aren't guaranteed to be visible, so if you improperly publish them, another thread could see them in a partially constructed state.) Is there any documentation on how/if the Scala compiler creates final (rather than non-final) backing fields for classes? I've looked through the language specification and searched the web but can't find any definitive answers. (In comparison the @scala.volatile annotation is documented to mark a field as volatile)

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• How does polymorphism work in Python?

  - by froadie

  I'm new to Python... and coming from a mostly Java background, if that accounts for anything. I'm trying to understand polymorphism in Python. Maybe the problem is that I'm expecting the concepts I already know to project into Python. But I put together the following test code: class animal(object): "empty animal class" class dog(animal): "empty dog class" myDog = dog() print myDog.__class__ is animal print myDog.__class__ is dog From the polymorphism I'm used to (e.g. java's instanceof), I would expect both of these statements to print true, as an instance of dog is an animal and also is a dog. But my output is: False True What am I missing?

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• Subscribing to a ObservableCollection via reflection

  - by Julian Lettner

  How can I subscribe to a ObservableCollection<??> without knowing the element type of the collection? Is there a way to do this without too many 'magic strings'? This is a question for the .NET version 3.5. I think 4.0 would make my life much easier, right? Type type = collection.GetType(); if(type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ObservableCollection<>)) { // I cannot cast the collection here ObservableCollection<object> x = collection; } Thanks for your time.

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• Unix tree convert to recursive php array

  - by Fordnox

  I have a response from remote server like this: /home/computer/Downloads |-- /home/computer/Downloads/Apple | `-- /home/computer/Downloads/Apple/Pad |-- /home/computer/Downloads/Empty_Folder `-- /home/computer/Downloads/Subfolder |-- /home/computer/Downloads/Subfolder/Empty `-- /home/computer/Downloads/Subfolder/SubSubFolder `-- /home/computer/Downloads/Subfolder/SubSubFolder/Test this is the output for command computer@athome:$ tree -df --noreport -L 5 /home/computer/Downloads/ I would like to parse this string to recursive php array or object, something like this. I would show only part of result to get the idea. array( 'title' => '/home/computer/Downloads', 'children' => array( 0 => array( 'title' => '/home/computer/Downloads/Apple', 'children' => array( ... ) ) ); Response from server can change according to scanned directory. Can someone help me write this function. Please note that this is response from remote server and php functions can not scan any remote dir.

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• Correctly parsing an ATOM feed

  - by Joseph

  I currently have setup a Python script that uses feedparser to read a feed and parse it. However, I have recently come across a problem with the date parsing. The feed I am reading contains <modified>2010-05-05T24:17:54Z</modified> - which comes up in Python as a datetime object - 2010-05-06 00:17:54. Notice the discrepancy: the feed entry was modified on the 5th of may, while python reads it as the 6th. So the question is why this is happening. Is the ATOM feed (that is, the one who created the feed) wrong by putting the time as 24:17:54, or is my python script wrong in the way it treats it. And can I solve this?

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• how to read the txt file from the database(line by line)

  - by Ranjana

  i have stored the txt file to sql server database . i need to read the txt file line by line to get the content in it. my code : DataTable dtDeleteFolderFile = new DataTable(); dtDeleteFolderFile = objutility.GetData("GetTxtFileonFileName", new object[] { ddlSelectFile.SelectedItem.Text }).Tables[0]; foreach (DataRow dr in dtDeleteFolderFile.Rows) { name = dr["FileName"].ToString(); records = Convert.ToInt32(dr["NoOfRecords"].ToString()); bytes = (Byte[])dr["Data"]; } FileStream readfile = new FileStream(Server.MapPath("txtfiles/" + name), FileMode.Open); StreamReader streamreader = new StreamReader(readfile); string line = ""; line = streamreader.ReadLine(); but here i have used the FileStream to read from the Particular path. but i have saved the txt file in byt format into my Database. how to read the txt file using the byte[] value to get the txt file content, instead of using the Path value.

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• ASP.NET data bind two-way, bi-directional from code behind

  - by Konrad

  Hello, so for two-way (bi-directional) databinding in ASP, we do this... <asp:textbox id="txtField" runat="server" text='<%# Bind("SomeField") %>'> </asp:textbox> SomeField is located on the DataSource of the DetailsView that serves as the container for the textbox. Alternatively I could do this from code-behind (using the textbox's OnDataBinding event): protected void SomeField_OnDataBinding(object sender, EventArgs e) { ((TextBox)sender).Text = Eval("SomeField").ToString(); } However, EVAL is read-only...how can I specify Bind (two-way) from code-behind?

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• Can SQLAlchemy DateTime Objects Only Be Naive?

  - by Sean M

  I am working with SQLAlchemy, and I'm not yet sure which database I'll use under it, so I want to remain as DB-agnostic as possible. How can I store a timezone-aware datetime object in the DB without tying myself to a specific database? Right now, I'm making sure that times are UTC before I store them in the DB, and converting to localized at display-time, but that feels inelegant and brittle. Is there a DB-agnostic way to get a timezone-aware datetime out of SQLAlchemy instead of getting naive datatime objects out of the DB?

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• Resolving type parameter values passed to ancester type using reflection

  - by Tom Tucker

  I've asked a similar question before, but this one is much more challenging. How do I find a value of a specific type parameter that is passed to an ancestor class or an interface implemented by one of its ancestor classes using reflection? I basically need to write a method that looks like this. // Return the value of the type parameter at the index passed to the parameterizedClass from the clazz. Object getParameterValue(Class<?> clazz, Class<?> parameterizedClass, int index) For the example below, getParameterValue(MyClass.class, Map.class, 1) would return String.class public class Foo<K, V> implements Map<K, V>{ } public class Bar<V> extends Foo<Integer, V> { } public class MyClass extends Bar<String> { } Thanks!

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• HTML5 offline video caching in mobile safari

  - by jj

  Sorry if this gets posted twice, but Safari crashed while posting the first version, and I don't see it in my profile. Anyway I can't seem to get Safari on the iPhone or iPad to offline cache videos. Everything else gets cached just fine when I go offline. The video file is obviously in the manifest, but I just get the broken arrow. Works fine in Safari desktop. Any clues? I've tried both object embed and the video tags.

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• Singleton Properties

  - by coffeeaddict

  Ok, if I create a singleton class and expose the singleton object through a public static property...I understand that. But my singleton class has other properties in it. Should those be static? Should those also be private? I just want to be able to access all properties of my singleton class by doing this: MySingletonClass.SingletonProperty.SomeProperty2 Where SingletonProperty returns me the single singleton instance. I guess my question is, how do you expose the other properties in the singleton class..make them private and then access them through your public singleton static property?

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