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• How do I use Declarations (type, inline, optimize) in Scheme?

  - by kunjaan

  How do I declare the types of the parameters in order to circumvent type checking? How do I optimize the speed to tell the compiler to run the function as fast as possible like (optimize speed (safety 0))? How do I make an inline function in Scheme? How do I use an unboxed representation of a data object? And finally are any of these important or necessary? Can I depend on my compiler to make these optimizations? thanks, kunjaan.

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• What is wrong with this simple type definition? (Expecting one more argument to...)

  - by fluteflute

  basic.hs: areaCircle :: Floating -> Floating areaCircle r = pi * r * r Command: *Main> :l basic.hs [1 of 1] Compiling Main ( Sheet1.hs, interpreted ) Sheet1.hs:2:15: Expecting one more argument to `Floating' In the type signature for `areaCircle': areaCircle :: Floating -> Floating Failed, modules loaded: none. I see that areaCircle :: Floating a => a -> a loads as expected. Why is the above version not acceptable?

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• Is it possible to specify a return type of "Derivative(of T)" for a MustOverride sub in VB.NET?

  - by Casey

  VB.NET 2008 .NET 3.5 I have two base classes that are MustInherit (partial). Let's call one class OrderBase and the other OrderItemBase. A specific type of order and order item would inherit from these classes. Let's call these WebOrder (inherits from OrderBase) and WebOrderItem (inherits from OrderItemBase). Now, in the grand scheme of things WebOrder is a composite class containing a WebOrderItem, like so: Public Class WebOrder Inherits OrderBase Public Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class In order to make sure any class that derives from OrderBase has the OrderItem property, I would like to do something like this in the OrderBase class: Public MustInherit Class OrderBase Public MustOverride Property OrderItem() as Derivative(Of OrderItemBase) End Class In other words, I want the derived class to be forced to contain a property that returns a derivative of OrderItemBase. Is this possible, or should I be using an entirely different approach?

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• How can the generic method called know the type of the generic return?

  - by Paulo Guedes

  I couldn't find a duplicate for this question for Java, although there are a lot of them for C#. I have this method: public <T> T getSomething() { // } According to the type of T, I will have a different return. For example: String a = getSomething(); int b = getSomething(); For a, my method will return a specific String. For b, it will return a specific int. And so on. It seems that this can be done with typeof() in C#. How can I achieve it in Java?

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• Which type of Rails model association should I use in this situation?

  - by jstayton

  I have two models/tables in my Rails application: discussions and comments. Each discussion has_many comments, and each comment belongs_to a discussion. My discussions table also includes a first_comment_id column and last_comment_id column for convenience and speed. I want to be able to call discussion.last_comment for the last comment model, but the following (in my discussion model) isn't working to make this happen: has_one :first_comment, :class_name => "Comment" has_one :last_comment, :class_name => "Comment" When I call discussion.last_comment, the following SQL is run: SELECT * FROM `comments` WHERE (`comments`.discussion_id = 1) LIMIT 1 It's using the discussions.id column to join against comments.discussion_id, when I want it to join discussions.last_comment_id against comments.id. Am I using the wrong type of association here? Thanks for your help!

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• Problem with number/type of arguments passed to an overloaded c++ constructor wrapped with swig.

  - by MiKo

  I am trying to wrap a c++ class (let's call it "Spam") written by someone else with swig to expose it to Python. After solving several problems, I am able to import the module in python, but when I try to create an object of such class I obtain the following error: foo = Spam.Spam('abc',3) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "Spam.py", line 96, in __init__ this = _Spam.new_Spam(*args) NotImplementedError: Wrong number of arguments for overloaded function 'new_Spam'. Possible C/C++ prototypes are: Spam(unsigned char *,unsigned long,bool,unsigned int,SSTree::io_action,char const *) Spam(unsigned char *,unsigned long,bool,unsigned int,SSTree::io_action) Spam(unsigned char *,unsigned long,bool,unsigned int) Spam(unsigned char *,unsigned long,bool) Spam(unsigned char *,unsigned long) Googling around, I realized that the error is probably caused by the type of the arguments and not by the number (which is quite confusing), but I still cannot identify. I suspect the problem lies in passing a string as the first argument, but have no idea on how to fix it (keep in mind that I know almost no c/c++).

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• C# Reflection - How can I tell if object o is of type KeyValuePair and then cast it?

  - by Logan

  Hi All I'm currently trying to write a Dump() method from LinqPad equivalent iin C# for my own amusment. I'm moving from Java to C# and this is an exercise rather than a business requirement. I've got almost everything working except for Dumping a Dictionary. The problem is that KeyValuePair is a Value type. For most other Value types I simply call the ToString method but this is insufficient as the KeyValuePair may contain Enumerables and other objects with undesirable ToString methods. So I need to work out if it's a KeyValuePair and then cast it. In Java I could use wildcard generics for this but I don't know the equivalent in C#. Your quest, given an object o, determine if it's a KeyValuePair and call Print on its key and value. Print(object o) { ... } Thanks!

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• How to look up an NHibernate entity's table mapping from the type of the entity?

  - by snicker

  Once I've mapped my domain in NHibernate, how can I reverse lookup those mappings somewhere else in my code? Example: The entity Pony is mapped to a table named "AAZF1203" for some reason. (Stupid legacy database table names!) I want to find out that table name from the NH mappings using only the typeof(Pony) because I have to write a query elsewhere. How can I make the following test pass? private const string LegacyPonyTableName = "AAZF1203"; [Test] public void MakeSureThatThePonyEntityIsMappedToCorrectTable() { string ponyTable = GetNHibernateTableMappingFor(typeof(Pony)); Assert.AreEqual(LegacyPonyTableName, ponyTable); } In other words, what does the GetNHibernateTableMappingFor(Type t) need to look like?

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• Why Is It That Generics Constraint Can't Be Casted to Its Derived Type?

  - by Ngu Soon Hui

  It is quite puzzling to find out that Generics Constraint Can't Be Casted to Its Derived Type. Let's say I have the following code: public abstract class BaseClass { public int Version { get { return 1; } } public string FixString { get; set; } public BaseClass() { FixString = "hello"; } public virtual int GetBaseVersion() { return Version; } } public class DeriveClass: BaseClass { public new int Version { get { return 2; } } } And guess what, this method will return a compilation error: public void FreeConversion<T>(T baseClass) { var derivedMe = (DeriveClass)baseClass; } I would have to cast the baseClass to object first before I can cast it to DerivedClass. Seems to me pretty ugly. Why this is so?

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• Using SSIS, how do you read a datetime field into a variable that is of Data Type string?

  - by Mark Kadlec

  This one has bugged me for the longest time and a great question to ask the Stackoverflow users I think. I have a rather large SSIS flow that uses a string variable to store the datetime. I would now like to dynamically read the datetime value from the database, but how would you construct the SSIS to do this? My first obvious thought would be to simply execute a SQL task to get the datetime and store it in the variable, but got the "differs from the current variable type" error. Is there a simple way to convert the database datetime into a String variable? Any help from the community would be appreciated,

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• What is the pythonic way to add type information to an object's attributes?

  - by Tikitu

  I'm building classes where I know the types of the attributes, but Python of course doesn't. While it's un-pythonic to want to tell it, supposing I do want to, is there an idiomatic way to do so? Why: I'm reading in serialised data (without type information) involving objects-nested-inside-objects. It's easy to put it into nested dictionaries, but I want it in objects of my class-types, to get the right behaviours as well as the data. For instance: suppose my class Book has an attribute isbn which I will fill with an ISBNumber object. My serialised data gives me the isbn as a string; I would like to be able to look at Book and say "That field should be filled by ISBNumber(theString)." Bonus glee for me if the solution can be applied to classes I get from someone else without editing their code.

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• is right to implement a business logic in the type binding DI framwork?

  - by Martino

  public IRedirect FactoryStrategyRedirect() { if (_PasswordExpired) { return _UpdatePasswordRedirectorFactory.Create(); } else { return _DefaultRedirectorFactory.Create(); } } This strategy factory method can be replaced with type binding and when clause: Bind<IRedirect>.To<UpdatePasswordRedirector>.When(c=> c.kernel.get<SomeContext>().PasswordExpired()) Bind<IRedirect>.To<DefaultRedirector>.When(c=> not c.kernel.get<SomeContext>().PasswordExpired()) I wonder which of the two approaches is the more correct. What are the pros and cons. Especially in the case in which the logic is more complex with more variables to test and more concrete classes to return. is right to implement a business logic in the binding?

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• Open generic interface types of open implementation don't equal interface type?

  - by George Mauer

  Here's a test that should, in my opinion be passing but is not. [TestMethod] public void can_get_open_generic_interface_off_of_implementor() { typeof(OpenGenericWithOpenService<>).GetInterfaces().First() .ShouldEqual(typeof(IGenericService<>)); } public interface IGenericService<T> { } public class OpenGenericWithOpenService<T> : IGenericService<T> { } Why does this not pass? Given Type t = typeof(OpenGenericWithOpenService<>) how do I get typeof(IGenericService<)? I'm generally curious, but if you're wondering what I'm doing, I'm writing a Structuremap convention that forwards all interfaces implemented by a class to the implementation (as a singleton).

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• In a C++ template, is it allowed to return an object with spesific type parameters?

  - by nieldw

  When I've got a template with certain type parameters, is it allowed for a function to return an object of this same template, but with different types? In other words, is the following allowed? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { /* Construct new Graph with apropriate decorators */ Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); /* ... */ return span; }; If this is not allowed, how can I accomplish the same kind of thing?

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• In Eclipse, how do I change the default modifiers in the class/type template?

  - by gustafc

  Eclipse's default template for new types (Window Preferences Code Style Code Templates New Java Files) looks like this: ${filecomment} ${package_declaration} ${typecomment} ${type_declaration} Creating a new class, it'll look something like this: package pkg; import blah.blah; public class FileName { // Class is accessible to everyone, and can be inherited } Now, I'm fervent in my belief that access should be as restricted as possible, and inheritance should be forbidden unless explicitly permitted, so I'd like to change the ${type_declaration} to declare all classes as final rather than public: package pkg; import blah.blah; final class FileName { // Class is only accessible in package, and can't be inherited } That seems easier said than done. The only thing I've found googling is a 2004 question on Eclipse's mailing list which was unanswered. So, the question in short: How can I change the default class/type modifiers in Eclipse? I'm using Eclipse Galileo (3.5) if that matters.

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• Is there any tool which can rearrange the css based on same type selector?

  - by metal-gear-solid

  I've big css where selector for same things are on different place. Is there any tool which can rearrange the css based on same type selector? This is just example. #main h2 { font-size: 2em; } #sidebar h3 { font-size: 2em; } #main h1 { font-size: 3em; } #sidebar h4 { font-size: 1.6em; } #main #box h2 { font-size: 2em; } #sidebar ul li { font-size: 1em; } it should arranged like this #main h1 { font-size: 3em; } #main h2 { font-size: 2em; } #main #box h2 { font-size: 2em; } #sidebar h3 { font-size: 2em; } #sidebar h4 { font-size: 1.6em; } #sidebar ul li { font-size: 1em; } if parent selector is same then all should be at same place.

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• c++: how can i read a file line by line to a string type variable?

  - by ufk

  Hiya. I'm trying to read a file line by line to a string type variable using the following code: #include <iostream> #include <fstream> ifstream file(file_name); if (!file) { cout << "unable to open file"; exit(1); } string line; while (!file.eof()) { file.getline(line,256); cout<<line; } file.close(); it won't compile when I try to use String class, only when i use char file[256] instead. how can I get line by line into a string class? thanks!

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• I serialized a C++ object, how to allocate memory for it without knowing what type it is?

  - by Neo_b

  Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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• Are the atomic builtins provided by gcc actually translated into the example code, or is that just f

  - by Jared P

  So I was reading http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html, and came across this: type __sync_and_and_fetch (type *ptr, type value, ...) type __sync_xor_and_fetch (type *ptr, type value, ...) type __sync_nand_and_fetch (type *ptr, type value, ...) These builtins perform the operation suggested by the name, and return the new value. That is, { *ptr op= value; return *ptr; } { *ptr = ~*ptr & value; return *ptr; } // nand Is this code literal? or is it just to explain what gcc is doing atomically using c-like syntax? And if this is the direct translation, can someone explain how it is atomic?

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• Which type of data can be garbage collected when app is in background?

  - by Neoh

  Let's say I start from activity A - activity B. While in activity B I press home to exit. After a long time, gc may be called because other apps take higher priority. My question is, which of the following type of data will be garbage collected (I'm pretty sure static fields can be garbage collected any time but I'm not sure about these): i) fields that are declared final or static final ii) intent and its data that I passed from activity A to activity B iii) onSavedInstanceState when orientation is changed during the app running I ask this because I want to ensure that my app won't crash when I restore activity B from background after a long period.

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• Can I have a type that's both, covariant and contravariant, i.e. fully fungible/changeable with sub

  - by Water Cooler v2

  Just a stupid question. I could try it out in 2 minutes, really. It's just that I have 1 GB RAM and have already got 2 instances of VS 2010 open on my desktop, with an instance of VS 2005, too. Opening another instance of VS 2010 would be an over kill. Can I have a type (for now forgetting its semantics) that can be covariant as well as contravariant? For e.g. public interface Foo<in out T> { void DoFooWith(T arg); } Off to Eric Lippert's blog for the meat and potatoes of variance in C# 4.0 as there's little else anywhere that covers adequate ground on the subject.

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• JPA 2.0 Provider Hibernate 3.6 for DB2 v9.5 type 2 driver is throwing exception in configuration prepration

  - by Deep Saurabh

  The JPA 2.0 Provider Hibernate is throwing exception while preparing configuration for entity manager factory, I am using DB2 v9.5 database and DB2 v9.5 JDBC type 2 driver . java.sql.SQLException: [IBM][JDBC Driver] CLI0626E getDatabaseMajorVersion is not supported in this version of DB2 JDBC 2.0 driver. at COM.ibm.db2.jdbc.app.SQLExceptionGenerator.throwNotSupportedByDB2(Unknown Source) at COM.ibm.db2.jdbc.app.DB2DatabaseMetaData.getDatabaseMajorVersion(Unknown Source) at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:117) at org.hibernate.cfg.Configuration.buildSettingsInternal(Configuration.java:2833) at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2829) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1840) at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:902) at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:57) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:48) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:32)

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• Delphi 2010 - Why can't I declare an abstract method with a generic type parameter?

  - by James

  I am trying to do the following in Delphi 2010: TDataConverter = class abstract public function Convert<T>(const AData: T): string; virtual; abstract; end; However, I keep getting the following compiler error: E2533 Virtual, dynamic and message methods cannot have type parameters I don't quite understand the reason why I can't do this. I can do this in C# e.g. public abstract class DataConverter { public abstract string Convert<T>(T data); } Anyone know the reasoning behind this?

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• Without using PECL or system() type functions, is there a way to look up DNS records using PHP?

  - by Navarr

  I'm working on creating a new type of email protocol, and in order to do that I had to set up an SRV DNS record for my domain. In promoting this protocol, I'll need to be able to discover if a given host uses my system (and if not fall back to an older protocol). So, is there a way to pull a DNS record (such as SRV) using PHP without using a PECL extension or running it through the linux command line (I already know I can ob_start() and system("host -t SRV hostname") but I'm looking for a better way, if it exists.)

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• Are these REST HTTP response codes right, and what about the Content-Type?

  - by talentedmrjones

  I'm writing a controller helper that sets the proper response headers for my REST controller action. It's pasted below and should be simplified enough for those who aren't familiar with Zend Framework to understand what I'm doing. My question is: Are these codes correct for their respective responses, and in the case of "access denied" do I use a 401 or 403? Also, in case of responding with an error, I understand I should be placing a message in the response body, but should I set the "Content-Type" to "text/plain"? <?php class App_Controller_Helper_RestResponse extends Zend_Controller_Action_Helper_Abstract { public function denied() { // 403 or 401? } public function notFound() { // 404 } public function created() { // 201 } public function deleted() { // 204 } public function redirect() { // 301 // new url } public function malformed() { // 400 } public function gone() { // 410 } }

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