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  • Why doesn't C# do "simple" type inference on generics?

    - by Ken Birman
    Just curious: sure, we all know that the general case of type inference for generics is undecidable. And so C# won't do any kind of subtyping at all: if Foo<T> is a generic, Foo<int> isn't a subtype of Foo<T>, or Foo<Object> or of anything else you might cook up. And sure, we all hack around this with ugly interface or abstract class definitions. But... if you can't beat the general problem, why not just limit the solution to cases that are easy. For example, in my list above, it is OBVIOUS that Foo<int> is a subtype of Foo<T> and it would be trivial to check. Same for checking against Foo<Object>. So is there some other deep horror that would creep forth from the abyss if they were to just say, aw shucks, we'll do what we can? Or is this just some sort of religious purity on the part of the language guys at Microsoft?

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  • how do I initialize a float to its max/min value?

    - by Faken
    How do I hard code an absolute maximum or minimum value for a float or double? I want to search out the max/min of an array by simply iterating through and catching the largest. There are also positive and negative infinity for floats, should I use those instead? If so, how do I denote that in my code?

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  • Undetermined type conversion in VB.NET 2008

    - by user337501
    I figured this would be a quick google, but extensive searching hasnt yielded any results. Everything about type conversion seems to dance around this concept. I want to get the type of variable "a", and make a new variable named "b" of that type. Otherwise I could have "a" as a type already declared and "b" simply as an Object, then try to cast "b" to the type of "a". Dim a As Integer Dim b As Whatever a Is OR TryCast(b, Whatever a Is) I would also like to make the conversion using a variable representation of the type, but cant find info on how to do that either. Sorta like: Dim a As Integer Dim b As Object Dim t As Type t = a.GetType() TryCast(b, t) Realizing I'm completely misusing TryCast here, I'm mostly trying to get my goal across. I figured it would be an easy quick thing to do but I cant really find any specific info on it. Any ideas?

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  • Javascript instanceof & typeof in GWT (JSNI)

    - by rybz
    Hi, I've encountered an curious problem while trying to use some objects through JSNI in GWT. Let's say we have javscript file with the function defined: test.js: function test(arg){ var type = typeof(arg); if (arg instanceof Array) alert('Array'); if (arg instanceof Object) alert('Object'); if (arg instanceof String) alert('String'); } And the we want to call this function user JSNI: public static native void testx()/ *-{ $wnd.test( new Array(1, 2, 3) ); $wnd.test( [ 1, 2, 3 ] ); $wnd.test( {val:1} ); $wnd.test( "Some text" ); }-*/; The questions are: why instanceof instructions will always return false? why typeof will always return "object" ? how to pass these objects so that they were recognized properly?

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  • Is it good practice to use std::size_t all over the place?

    - by dehmann
    I have a lot of constants in my code that are unsigned numbers, e.g. counters, frequency cutoffs, lengths, etc. I started using std::size_t for all of these, instead of int or unsigned int. Is that the right thing to do? I started it because the STL containers use it for their sizes, it's used for string position, etc.

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  • Bound a treeview control to user-defined complex type using EF 4

    - by GIbboK
    Hi, I use Asp.net, SQL 2008 and EF 4. I need display hierarchy data in a treeview control, Data is stored in a DB that use HierarchyId. Unfortunately, EF4 doesn't support HierarchyId. So in this case, I thought to have a stored procedure that deals with my hierarchy and return a result set back to EF that EF4 can turn into a collection of user-defined complex type that can then be bound directly to the treeview control. I imported a SPROC in EF 4 using Import Function and now I have a Complex DataType called: CategoryHierarchy_Result An image of my Model: Here some data from the Complex Type (in a GridView for example GridView1.DataSource = context.CategoryHierarchy(1);): My questions is: How to display my data from my Complex Type in a TreeView Control, showing a Tree structure that respect CategoryNodeString? I am a beginner an I never use TreeView before, any help or resource would be appreciated! Thanks!. Here some useful resource: http://www.robbagby.com/entity-framework/entity-framework-modeling-action-stored-procedures/

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  • Implicit parameter in Scalaz

    - by Thomas Jung
    I try to find out why the call Ø in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => Ø case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[String]{ def y = "y" } } trait Xs{ def ys[T](implicit x : X[T]) = x.y } class A extends Xs{ def z[B](implicit x : X[B]) : B = ys //the call Ø } Which produces: import X._ scala> new A().z[Int] res0: Int = 42 scala> new A().z[String] res1: String = y Is this valid? Can I achieve the same result with fewer steps?

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  • Perfect hash in Scala.

    - by Lukasz Lew
    I have some class C: class C (...) { ... } I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id: object C { var id_counter = 0 } In primary constructor of C, with each creation of C I want to remember global counter value and increase it. Question 1: How to do it? Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id. Question 2: Is it possible to have it with type safety?

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  • LINQ Group By to project into a non-anonymous type?

    - by vikp
    Hi, I have the following LINQ example: var colorDistribution = from product in ctx.Products group product by product.Color into productColors select new { Color = productColors.Key, Count = productColors.Count() }; All this works and makes perfect sense. What I'm trying to achieve is to group by into a strong type instead of anonymous type. For example I have a ProductColour class and I would like to Group into a List<ProductColour> Is this possible? Thank you

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  • Best way to determine variable type and treat each one differently in F#

    - by James Black
    I have a function that will create a select where clause, but right now everything has to be a string. I would like to look at the variable passed in and determine what type it is and then treat it properly. For example, numeric values don't have single quotes around them, option type will either be null or have some value and boolean will actually be zero or one. member self.BuildSelectWhereQuery (oldUser:'a) = let properties = List.zip oldUser.ToSqlValuesList sqlColumnList let init = false, new StringBuilder() let anyChange, (formatted:StringBuilder) = properties |> Seq.fold (fun (anyChange, sb) (oldVal, name) -> match(anyChange) with | true -> true, sb.AppendFormat(" AND {0} = '{1}'", name, oldVal) | _ -> true, sb.AppendFormat("{0} = '{1}'", name, oldVal) ) init formatted.ToString() Here is one entity: type CityType() = inherit BaseType() let mutable name = "" let mutable stateId = 0 member this.Name with get() = name and set restnameval=name <- restnameval member this.StateId with get() = stateId and set stateidval=stateId <- stateidval override this.ToSqlValuesList = [this.Name; this.StateId.ToString()] So, if name was some other value besides a string, or stateId can be optional, then I have two changes to make: How do I modify ToSqlValuesList to have the variable so I can tell the variable type? How do I change my select function to handle this? I am thinking that I need a new function does the processing, but what is the best FP way to do this, rather than using something like typeof?

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  • Access to an inner type

    - by sohum
    A colleague of mine posted a question on an internal forum which got me thinking about whether this was possible through C#. Basically, he's got an interface as follows: public interface IProvider<T> { T GetT(); } Is it possible to use something that implements that interface as a type parameter to another generic class and have access to the type T without re-specifying it? For example: public class Foo<P> where P : IProvider<T> { P p; T GetInnerT() { return p.GetT(); } } This does not compile, because the type T is not defined and hence can't be used as a parameter for IProvider. Is something like this even possible? Just curious!

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  • c# Reflection - Find the Generic Type of a Collection

    - by Andy Clarke
    Hi, I'm reflecting a property 'Blah' its Type is ICollection public ICollection<string> Blah { get; set; } private void button1_Click(object sender, RoutedEventArgs e) { var pi = GetType().GetProperty("Blah"); MessageBox.Show(pi.PropertyType.ToString()); } This gives me (as you'd expect!) ICollection<string> ... But really I want to get the collection type i.e. ICollection (rather than ICollection<string>) - does anyone know how i'd do this please?

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  • Can't get KnownType to work with WCF

    - by Kelly Cline
    I have an interface and a class defined in separate assemblies, like this: namespace DataInterfaces { public interface IPerson { string Name { get; set; } } } namespace DataObjects { [DataContract] [KnownType( typeof( IPerson ) ) ] public class Person : IPerson { [DataMember] public string Name { get; set; } } } This is my Service Interface: public interface ICalculator { [OperationContract] IPerson GetPerson ( ); } When I update my Service Reference for my Client, I get this in the Reference.cs: public object GetPerson() { return base.Channel.GetPerson(); I was hoping that KnownType would give me IPerson instead of "object" here. I have also tried [KnownType( typeof( Person ) ) ] with the same result. I have control of both client and server, so I have my DataObjects (where Person is defined) and DataInterfaces (where IPerson is defined) assemblies in both places. Is there something obvious I am missing? I thought KnownType was the answer to being able to use interfaces with WCF. ----- FURTHER INFORMATION ----- I removed the KnownType from the Person class and added [ServiceKnownType( typeof( Person ) ) ] to my service interface, as suggested by Richard. The client-side proxy still looks the same, public object GetPerson() { return base.Channel.GetPerson(); , but now it doesn't blow up. The client just has an "object", though, so it has to cast it to IPerson before it is useful. var person = client.GetPerson ( ); Console.WriteLine ( ( ( IPerson ) person ).Name );

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  • Why do C++ streams use char instead of unsigned char?

    - by Johannes Schaub - litb
    I've always wondered why the C++ Standard library has instantiated basic_[io]stream and all its variants using the char type instead of the unsigned char type. char means (depending on whether it is signed or not) you can have overflow and underflow for operations like get(), which will lead to implementation-defined value of the variables involved. Another example is when you want to output a byte, unformatted, to an ostream using its put function. Any ideas? Note: I'm still not really convinced. So if you know the definitive answer, you can still post it indeed.

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  • How to change a variable type in C#?

    - by Mosho Mulan
    I wanted to use something like this: if(x==5) { var mydb= ........ ; } else { var mydb = ........ ; } but it didn't work because I can't declare a variable inside if statement. So I tried to do this: var mydb; if (x==5) { mydb= ............. ; } else { mydb=.............; } but id didn't work either because I had to initialize the variable (mydb). So the question is: I don't necessarily know the type of the variable, can I declare it anyway and then change the type inside the if statement?

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  • Converting between unsigned and signed int safely

    - by polemic
    I have an interface between a client and a server where a client sends (1) an unsigned value, and (2) a flag which indicates if value is signed/unsigned. Server would then static cast unsigned value to appropriate type. I later found out that this is implementation defined behavior and I've been reading about it but I couldn't seem to find an appropriate solution that's completely safe? I've read about type punning, pointer conversions, and memcpy. Would simply using a union type work? A UnionType containing signed and unsigned int, along with the signed/unsigned flag. For signed values, client sets the signed part of the union, and server reads the signed part. Same for the unsigned part. Or am I completely misunderstanding something? Side question: how do I know the specific behavior in this case for a specific scenario, e.g. windriver diab on PPC? I'm a bit lost on how to find such documentation.

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  • Is there a term for this concept, and does it exist in a static-typed language?

    - by Strilanc
    Recently I started noticing a repetition in some of my code. Of course, once you notice a repetition, it becomes grating. Which is why I'm asking this question. The idea is this: sometimes you write different versions of the same class: a raw version, a locked version, a read-only facade version, etc. These are common things to do to a class, but the translations are highly mechanical. Surround all the methods with lock acquires/releases, etc. In a dynamic language, you could write a function which did this to an instance of a class (eg. iterate over all the functions, replacing them with a version which acquires/releases a lock.). I think a good term for what I mean is 'reflected class'. You create a transformation which takes a class, and returns a modified-in-a-desired-way class. Synchronization is the easiest case, but there are others: make a class immutable [wrap methods so they clone, mutate the clone, and include it in the result], make a class readonly [assuming you can identify mutating methods], make a class appear to work with type A instead of type B, etc. The important part is that, in theory, these transformations make sense at compile-time. Even though an ActorModel<T> has methods which change depending on T, they depend on T in a specific way knowable at compile-time (ActorModel<T> methods would return a future of the original result type). I'm just wondering if this has been implemented in a language, and what it's called.

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  • Why do some people prefer "T const&" over "const T&"?

    - by Michael Aaron Safyan
    So, I realize that const T& and T const& are identical and both mean a reference to a const T. In both cases, the reference is also constant (references cannot be reassigned, unlike pointers). I've observed, in my somewhat limited experience, that most C++ programmers use const T&, but I have come across a few people who use T const&. Is this just a personal preference? Why is one chosen over the other?

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  • C# 4.0 dynamics

    - by mehanik
    Hi. Code bellow is working well until I have class ClassSameAssembly in same assembly as class Program. But when I move class ClassSameAssembly to separate assembly I have runtime error. Is it posible to resolve it? using System; namespace ConsoleApplication2 { public static class ClassSameAssembly { public static dynamic GetValues() { return new { Name = "Michael", Age = 20 }; } } internal class Program { private static void Main(string[] args) { var d = ClassSameAssembly.GetValues(); Console.WriteLine("{0} is {1} years old", d.Name, d.Age); } } }

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  • Calling Object Methods in Code

    - by Mister R2
    I'm a bit new to PHP, and I'm more experienced with strongly-typed languages such as JAVA, C# or C++.I'm currently writing a web tool in PHP, and I am having an issue trying to do what I want. The simple idea of what I want to do in code is run through some emails I used PHP-IMAP to get. I then create email objects (a class I defined), and put them in an array. Later on the code, however, I cycle through those emails to display them. However, as you might have guessed I'd have an issue with, I try to use an Email Class object method in that later loop -- and I'm pretty sure PHP doesn't know that the variables in the array happen to be Email Class objects! I wrote a toString method, and I want to call it in the loop. While I don't need to do this for the final version of this tool, I would like to find out what I'm missing. This is the class and the loop where I'm calling the method: include 'imap_email_interface.php'; class ImapEmail implements imap_email_interface { // Email data var $msgno; var $to; var $from; var $subject; var $body; var $attachment; // Email behavior /* PHP 4 ~ legacy constructor */ public function ImapEmail($message_number) { $this->__construct(); $this->msgno = $message_number; } /* PHP 5 Constructor */ public function __construct($message_number) { $this->msgno = $message_number; } public function send($send_to) { // Not Yet Needed! Seriously! } public function setHeaderDirectly($TO, $FROM, $SUBJECT) { $this->to = $TO; $this->from = $FROM; $this->subject = $SUBJECT; } public function setHeaderIndirectly($HEADER) { if (isset($HEADER->to[0]->personal)) $this->to = '"'.$HEADER->to[0]->personal.'", '.$HEADER->to[0]->mailbox.'@'.$HEADER->to[0]->host; else $this->to = $HEADER->to[0]->mailbox.'@'.$HEADER->to[0]->host; $this->from = '"'.$HEADER->from[0]->personal.'", '.$HEADER->from[0]->mailbox.'@'.$HEADER->from[0]->host; $this->subject = $HEADER->subject; } public function setBody($BODY) { $this->body = $BODY; } public function setAttachment($ATTCH) { $this->attachment = $ATTCH; } public function toString() { $str = '[TO]: ' . $this->to . '<br />' . '[FROM]: ' . $this->from . '<br />' . '[SUBJECT]: ' . $this->subject . '<br />'; $str .= '[Attachment]: '.$this->attachment.'<br />'; return $str; } } ?> The Loop: foreach ($orderFileEmails as $x) { $x->toString(); echo '<br /><br />'; } Any ideas?

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