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  • Indirect load of type fails in PowerShell

    - by Dan
    When invoking [System.Configuration.ConfigurationManager]::GetSection("MySection") from within a PowerShell prompt, it throws an exception because the assembly containing the type represented by "MySection" in the app config is unable to be loaded. However, I have previously loaded the assembly containing that type, and I am even able to instantiate the type directly using 'new-object'. How is the ConfigurationManager resolving types such that the assemblies already loaded into the PowerShell app domain are not visible to it?

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  • C#: Determine Type for (De-)Serialization

    - by dbemerlin
    Hi, i have a little problem implementing some serialization/deserialization logic. I have several classes that each take a different type of Request object, all implementing a common interface and inheriting from a default implementation: This is how i think it should be: Requests interface IRequest { public String Action {get;set;} } class DefaultRequest : IRequest { public String Action {get;set;} } class LoginRequest : DefaultRequest { public String User {get;set;} public String Pass {get;set;} } Handlers interface IHandler<T> { public Type GetRequestType(); public IResponse HandleRequest(IModel model, T request); } class DefaultHandler<T> : IHandler<T> // Used as fallback if the handler cannot be determined { public Type GetRequestType() { return /* ....... how to get the Type of T? ((new T()).GetType()) ? .......... */ } public IResponse HandleRequest(IModel model, T request) { /* ... */ } } class LoginHandler : DefaultHandler<LoginRequest> { public IResponse HandleRequest(IModel mode, LoginRequest request) { } } Calling class Controller { public ProcessRequest(String action, String serializedRequest) { IHandler handler = GetHandlerForAction(action); IRequest request = serializer.Deserialize<handler.GetRequestType()>(serializedRequest); handler(this.Model, request); } } Is what i think of even possible? My current Solution is that each handler gets the serialized String and is itself responsible for deserialization. This is not a good solution as it contains duplicate code, the beginning of each HandleRequest method looks the same (FooRequest request = Deserialize(serializedRequest); + try/catch and other Error Handling on failed deserialization). Embedding type information into the serialized Data is not possible and not intended. Thanks for any Hints.

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  • Obtain container type from (its) iterator type in C++ (STL)

    - by KRao
    It is easy given a container to get the associated iterators, example: std::vector<double>::iterator i; //An iterator to a std::vector<double> I was wondering if it is possible, given an iterator type, to deduce the type of the "corresponding container" (here I am assuming that for each container there is one and only one (non-const) iterator). More precisely, I would like a template metafunction that works with all STL containers (without having to specialize it manually for each single container) such that, for example: ContainerOf< std::vector<double>::iterator >::type evaluates to std::vector<double> Is it possible? If not, why? Thank you in advance for any help!

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  • Dynamically loading type in Silverlight with Type.GetType()

    - by ondesertverge
    Trying to specify the assembly name like this: Type.GetType(string.Format("{0}.{1}, {0}", widget.Assembly, widget.Class)); Throws this: The requested assembly version conflicts with what is already bound in the app domain or specified in the manifest Trying it without the the assembly: Type.GetType(string.Format("{0}.{1}", widget.Assembly, widget.Class)); Returns null. I am looking for a way to instantiate a class using it's fully qualified name in Silverlight 4.0. Thanks.

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  • Unable to cast object of type MyObject to type MyObject

    - by Robert W
    I have this scenario where a webservice method I'm consuming in C# returns a Business object, when calling the webservice method with the following code I get the exception "Unable to cast object of type ContactInfo to type ContactInfo" in the reference.cs class of the web reference Code: ContactInfo contactInfo = new ContactInfo(); Contact contact = new Contact(); contactInfo = contact.Load(this.ContactID.Value); Any help would be much appreciated.

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  • Object of type "X" cannot be converted to object of type "X"

    - by Benjol
    (Can't believe this hasn't already been asked, but I can't find a dup) In Visual Studio with lots of projects, when I first open the solution, I sometimes get the warning Object of type "X" cannot be converted to object of type "X". Generally rebuilding seems to make it go away, but does anyone know what this is caused by, and how to avoid it? UPDATE I read somewhere that deleting all your resx files and rebuilding can help. I unthinkingly tried this. Not a good idea...

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  • How to find out if an object is of <type> or a decendant of <type>

    - by Vaccano
    I have the following code: foreach (var control in this.Controls) { } I want to do something like control.Hide() in there. But the items in the this.Controls collection are not of type Control (they are Object). I can't seem to remember the safe way to cast this to call hide if it is really of type Control and do nothing otherwise. (I am a transplanted delphi programmer and I keep thinking something like control is Control.)

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  • Creating a Type object corresponding to a generic type

    - by Alexey Romanov
    In Java, how can I construct a Type object for Map<String, String>? System.out.println(Map<String, String>.class); doesn't compile. One workaround I can think of is private Map<String, String> dummy() { throw new Error(); } Type mapStringString = Class.forName("ThisClass").getMethod("dummy", null).getGenericReturnType(); Is this the correct way?

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  • changing restriction on simple type in extended complex type

    - by rotary_engine
    I am trying to create a schema that has 2 address types. The first AdressType requires an element Line 1 to have a value at least 10 characters. The second type OtherAdressType derives from this with the same elements, but does not require a value for Line 1. I've tried different ways but always get schema errors, this error is: Invalid particle derivation by restriction - 'Derived element '{namespace}:Line1' is not a valid restriction of base element '{namespace}:Line1' according to Elt:Elt -- NameAndTypeOK.'. If I add a type xs:string to OtherAdressType:Line1 then I get other errors. <xs:complexType name="AdressType"> <xs:sequence> <xs:element name="Line1" minOccurs="1" maxOccurs="1"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:minLength value="10" /> </xs:restriction> </xs:simpleType> </xs:element> <xs:element name="Line2" type="xs:string" minOccurs="1" maxOccurs="1" /> </xs:sequence> </xs:complexType> <xs:complexType name="OtherAdressType"> <xs:complexContent> <xs:restriction base="AdressType"> <xs:sequence> <xs:element name="Line1" nillable="true"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:minLength value="0" /> </xs:restriction> </xs:simpleType> </xs:element> <xs:element name="Line2" type="xs:string" minOccurs="1" maxOccurs="1" /> </xs:sequence> </xs:restriction> </xs:complexContent> </xs:complexType>

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  • Display a input type=file over another input type=file

    - by Kevin Sedgley
    WARNING: Lengthy description coming up! I have written an uploader based upon APC progress uploader for PHP. This works fine and dandy, but the script as a whole (apc etc) is intended to be used only for those with Javascript. To achieve this, I have searched for any input type=file, and replaced these with an absolutely positioned form that appears over the original area where the old file input area was. The reasons for this are so the new uploader can submit to a hidden in page IFrame has to be in a seperate <form> in order to submit to the APC reciever to display the progress upload bar. allows it to be used within any form with an input type=file throughout the site I have used JQuery to do this, with the following code: Original HTML form code: <div><input type="file" name="media" id="media" /></div> Find position of div block code: // get the parent div, and properties thereof parentDiv = $(this).closest('div'); w = $(parentDiv).width(); h = $(parentDiv).height(); loc = $(parentDiv).offset(); Locate new block over old block: $('#_sender').appendTo('body').css({left:loc.left,top:loc.top,position:'absolute',zIndex:400,height:h,width:w}).show(); This works fine, and shows over the old block OK. The problem: When other elements in the DOM before or above it change (in this case a "tree view" selector is pushing the old block down) the new upload form gets moved over other elements. Is there a JQuery (or JS) method for changing this upon DOM change? Some kind of .onchange for the page?! Or an .onmove for the original block? Thanks in advance you lovely people Before DOM change: . After: .

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  • Bind postback data from a strong type view of type List<T>

    - by Robert Koritnik
    I have a strong type view of type List<List<MyViewModelClass>> The outer list will always have two lists of List<MyViewModelClass>. For each of the two outer lists I want to display a group of checkboxes. Each set can have an arbitrary number of choices. My view model class looks similar to this: public class MyViewModelClass { public Area Area { get; set; } public bool IsGeneric { get; set; } public string Code { get; set; } public bool IsChecked { get; set; } } So the final view will look something like: Please select those that apply: First set of choices: x Option 1 x Option 2 x Option 3 etc. Second set of choices: x Second Option 1 x Second Option 2 x Second Option 3 x Second Option 4 etc. Checkboxes should display MyViewModelClass.Area.Name, and their value should be related to MyViewModelClass.Area.Id. Checked state is of course related to MyViewModel.IsChecked. Question I wonder how should I use Html.CheckBox() or Html.CheckBoxFor() helper to display my checkboxes? I have to get these values back to the server on a postback of course. I would like to have my controller action like one of these: public ActionResult ConsumeSelections(List<List<MyViewModelClass>> data) { // process data } public ActionResult ConsumeSelections(List<MyViewModelClass> first, List<MyViewModelClass> second) { // process data } If it makes things simpler, I could make a separate view model type like: public class Options { public List First { get; set; } public List Second { get; set; } } As well as changing my first version of controller action to: public ActionResult ConsumeSelections(Options data) { // process data }

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  • Declaring an object of a conditional type with a System.Type

    - by Chapso
    I am attempting to launch a specific form depending on the selected node of a treeview on the doubleclick event. The code I need to use to launch the form is a little bulky becuase I have to ensure that the form is not disposed, and that the form is not already open, before launching a new instance. I'd like to have all of this checking happen in one place at the end of the function, which means that I have to be able to pass the right form type to the code at the end. I'm trying to do this with a System.Type, but that doesn't seem to be working. Could someone point me in the right direction, please? With TreeView.SelectedNode Dim formType As Type Select Case .Text Case "Email to VPs" formType = EmailForm.GetType() Case "Revise Replacers" formType = DedicatedReplacerForm.GetType() Case "Start Email" formType = EmailForm.GetType() End Select Dim form As formType Dim form As formType Try form = CType(.Tag, formType) If Not form.IsDisposed Then form.Activate() Exit Sub End If Catch ex As NullReferenceException 'This will error out the first time it is run as the form has not yet ' been defined. End Try form = New formType form.MdiParent = Me .Tag = form CType(TreeView.SelectedNode.Tag, Form).Show() End With

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  • Why can't these generic type parameters be inferred?

    - by Jon M
    Given the following interfaces/classes: public interface IRequest<TResponse> { } public interface IHandler<TRequest, TResponse> where TRequest : IRequest<TResponse> { TResponse Handle(TRequest request); } public class HandlingService { public TResponse Handle<TRequest, TResponse>(TRequest request) where TRequest : IRequest<TResponse> { var handler = container.GetInstance<IHandler<TRequest, TResponse>>(); return handler.Handle(request); } } public class CustomerResponse { public Customer Customer { get; set; } } public class GetCustomerByIdRequest : IRequest<CustomerResponse> { public int CustomerId { get; set; } } Why can't the compiler infer the correct types, if I try and write something like the following: var service = new HandlingService(); var request = new GetCustomerByIdRequest { CustomerId = 1234 }; var response = service.Handle(request); // Shouldn't this know that response is going to be CustomerResponse? I just get the 'type arguments cannot be inferred' message. Is this a limitation with generic type inference in general, or is there a way to make this work?

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  • warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’

    - by pyz
    code: #include <stdio.h> #include <stdlib.h> #include <netdb.h> #include <sys/socket.h> int main(int argc, char **argv) { char *ptr, **pptr; struct hostent *hptr; char str[32]; //ptr = argv[1]; ptr = "www.google.com"; if ((hptr = gethostbyname(ptr)) == NULL) { printf("gethostbyname error for host:%s\n", ptr); } printf("official hostname:%s\n", hptr->h_name); for (pptr = hptr->h_aliases; *pptr != NULL; pptr++) printf(" alias:%s\n", *pptr); switch (hptr->h_addrtype) { case AF_INET: case AF_INET6: pptr = hptr->h_addr_list; for (; *pptr != NULL; pptr++) printf(" address:%s\n", inet_ntop(hptr->h_addrtype, *pptr, str, sizeof(str))); break; default: printf("unknown address type\n"); break; } return 0; } compiler output below: zhumatoMacBook:CProjects zhu$ gcc gethostbynamedemo.c gethostbynamedemo.c: In function ‘main’: gethostbynamedemo.c:31: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’

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  • Creating a Document Library with Content Type in code

    - by David Jacobus
    Originally posted on: http://geekswithblogs.net/djacobus/archive/2013/10/15/154360.aspxIn the past, I have shown how to create a list content type and add the content type to a list in code.  As a Developer, many of the artifacts which we create are widgets which have a List or Document Library as the back end.   We need to be able to create our applications (Web Part, etc.) without having the user involved except to enter the list item data.  Today, I will show you how to do the same with a document library.    A summary of what we will do is as follows:   1.   Create an Empty SharePoint Project in Visual Studio 2.   Add a Code Folder in the solution and Drag and Drop Utilities and Extensions Libraries to the solution 3.   Create a new Feature and add and event receiver  all the code will be in the event receiver 4.   Add the fields which will extend the built-in Document content type 5.   If the Content Type does not exist, Create it 6.   If the Document Library does not exist, Create it with the new Content Type inherited from the Document Content Type 7.   Delete the Document Content Type from the Library (as we have a new one which inherited from it) 8.   Add the fields which we want to be visible from the fields added to the new Content Type   Here we go:   Create an Empty SharePoint Project in Visual Studio      Add a Code Folder in the solution and Drag and Drop Utilities and Extensions Libraries to the solution       The Utilities and Extensions Library will be part of this project which I will provide a download link at the end of this post.  Drag and drop them into your project.  If Dragged and Dropped from windows explorer you will need to show all files and then include them in your project.  Change the Namespace to agree with your project.   Create a new Feature and add and event receiver  all the code will be in the event receiver.  Here We added a new Feature called “CreateDocLib”  and then right click to add an Event Receiver All of our code will be in this Event Receiver.  For this Demo I will only be using the Feature Activated Event.      From this point on we will be looking at code!    We are adding two constants for use columGroup (How we want SharePoint to Group them, usually Company Name) and ctName(ContentType Name)  using System; using System.Runtime.InteropServices; using System.Security.Permissions; using Microsoft.SharePoint; namespace CreateDocLib.Features.CreateDocLib { /// <summary> /// This class handles events raised during feature activation, deactivation, installation, uninstallation, and upgrade. /// </summary> /// <remarks> /// The GUID attached to this class may be used during packaging and should not be modified. /// </remarks> [Guid("56e6897c-97c4-41ac-bc5b-5cd2c04f2dd1")] public class CreateDocLibEventReceiver : SPFeatureReceiver { const string columnGroup = "DJ"; const string ctName = "DJDocLib"; } }     Here we are creating the Feature Activated event.   Adding the new fields (Site Columns) ,  Testing if the Content Type Exists, if not adding it.  Testing if the document Library exists, if not adding it.   #region DocLib public override void FeatureActivated(SPFeatureReceiverProperties properties) { using (SPWeb spWeb = properties.GetWeb() as SPWeb) { //add the fields addFields(spWeb); //add content type SPContentType testCT = spWeb.ContentTypes[ctName]; // we will not create the content type if it exists if (testCT == null) { //the content type does not exist add it addContentType(spWeb, ctName); } if ((spWeb.Lists.TryGetList("MyDocuments") == null)) { //create the list if it dosen't to exist CreateDocLib(spWeb); } } } #endregion The addFields method uses the utilities library to add site columns to the site. We can add as many fields within this method as we like. Here we are adding one for demonstration purposes. Icon as a Url type.  public void addFields(SPWeb spWeb) { Utilities.addField(spWeb, "Icon", SPFieldType.URL, false, columnGroup); }The addContentType method add the new Content Type to the site Content Types. We have already checked to see that it does not exist. In addition, here is where we add the linkages from our site columns previously created to our new Content Type   private static void addContentType(SPWeb spWeb, string name) { SPContentType myContentType = new SPContentType(spWeb.ContentTypes["Document"], spWeb.ContentTypes, name) { Group = columnGroup }; spWeb.ContentTypes.Add(myContentType); addContentTypeLinkages(spWeb, myContentType); myContentType.Update(); } Here we are adding just one linkage as we only have one additional field in our Content Type public static void addContentTypeLinkages(SPWeb spWeb, SPContentType ct) { Utilities.addContentTypeLink(spWeb, "Icon", ct); } Next we add the logic to create our new Document Library, which we have already checked to see if it exists.  We create the document library and turn on content types.  Add the new content type and then delete the old “Document” content types.   private void CreateDocLib(SPWeb web) { using (var site = new SPSite(web.Url)) { var web1 = site.RootWeb; var listId = web1.Lists.Add("MyDocuments", string.Empty, SPListTemplateType.DocumentLibrary); var lib = web1.Lists[listId] as SPDocumentLibrary; lib.ContentTypesEnabled = true; var docType = web.ContentTypes[ctName]; lib.ContentTypes.Add(docType); lib.ContentTypes.Delete(lib.ContentTypes["Document"].Id); lib.Update(); AddLibrarySettings(web1, lib); } }  Finally, we set some document library settings on our new document library with the AddLibrarySettings method. We then ensure that the new site column is visible when viewed in the browser.  private void AddLibrarySettings(SPWeb web, SPDocumentLibrary lib) { lib.OnQuickLaunch = true; lib.ForceCheckout = true; lib.EnableVersioning = true; lib.MajorVersionLimit = 5; lib.EnableMinorVersions = true; lib.MajorWithMinorVersionsLimit = 5; lib.Update(); var view = lib.DefaultView; view.ViewFields.Add("Icon"); view.Update(); } Okay, what's cool here: In a few lines of code, we have created site columns, A content Type, a document library. As a developer, I use this functionality all the time. For instance, I could now just add a web part to this same solutionwhich uses this document Library. I love SharePoint! Here is the complete solution: Create Document Library Code

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  • Type Conversion in JPA 2.1

    - by delabassee
    The Java Persistence 2.1 specification (JSR 338) adds support for various new features such as schema generation, stored procedure invocation, use of entity graphs in queries and find operations, unsynchronized persistence contexts, injection into entity listener classes, etc. JPA 2.1 also add support for Type Conversion methods, sometime called Type Converter. This new facility let developers specify methods to convert between the entity attribute representation and the database representation for attributes of basic types. For additional details on Type Conversion, you can check the JSR 338 Specification and its corresponding JPA 2.1 Javadocs. In addition, you can also check those 2 articles. The first article ('How to implement a Type Converter') gives a short overview on Type Conversion while the second article ('How to use a JPA Type Converter to encrypt your data') implements a simple use-case (encrypting data) to illustrate Type Conversion. Mission critical applications would probably rely on transparent database encryption facilities provided by the database but that's not the point here, this use-case is easy enough to illustrate JPA 2.1 Type Conversion.

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  • Is there an imperative language with a Haskell-like type system?

    - by Graham Kaemmer
    I've tried to learn Haskell a few times over the last few years, and, maybe because I know mainly scripting languages, the functional-ness of it has always bothered me (monads seem like a huge mess for doing lots of I/O). However, I think it's type system is perfect. Reading through a guide to Haskell's types and typeclasses (like this), I don't really see a reason why they would require a functional language, and furthermore, they seem like they would be perfect for an industry-grade object-oriented language (like Java). This all begs the question: has anyone ever taken Haskell's typing system and made a imperative, OOP language with it? If so, I want to use it.

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  • data validation on wpf passwordbox:type password, re-type password

    - by black sensei
    Hello Experts !! I've built a wpf windows application in with there is a registration form. Using IDataErrorInfo i could successfully bind the field to a class property and with the help of styles display meaningful information about the error to users.About the submit button i use the MultiDataTrigger with conditions (Based on a post here on stackoverflow).All went well. Now i need to do the same for the passwordbox and apparently it's not as straight forward.I found on wpftutorial an article and gave it a try but for some reason it wasn't working. i've tried another one from functionalfun. And in this Functionalfun case the properties(databind,databound) are not recognized as dependencyproperty even after i've changed their name as suggested somewhere in the comments plus i don't have an idea whether it will work for a windows application, since it's designed for web. to give you an idea here is some code on textboxes <Window.Resources> <data:General x:Key="recharge" /> <Style x:Key="validButton" TargetType="{x:Type Button}" BasedOn="{StaticResource {x:Type Button}}" > <Setter Property="IsEnabled" Value="False"/> <Style.Triggers> <MultiDataTrigger> <MultiDataTrigger.Conditions> <Condition Binding="{Binding ElementName=txtRecharge, Path=(Validation.HasError)}" Value="false" /> </MultiDataTrigger.Conditions> <Setter Property="IsEnabled" Value="True" /> </MultiDataTrigger> </Style.Triggers> </Style> <Style x:Key="txtboxerrors" TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}"> <Style.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> <Setter Property="Validation.ErrorTemplate"> <Setter.Value> <ControlTemplate> <DockPanel LastChildFill="True"> <TextBlock DockPanel.Dock="Bottom" FontSize="8" FontWeight="ExtraBold" Foreground="red" Padding="5 0 0 0" Text="{Binding ElementName=showerror, Path=AdornedElement.(Validation.Errors)[0].ErrorContent}"></TextBlock> <Border BorderBrush="Red" BorderThickness="2"> <AdornedElementPlaceholder Name="showerror" /> </Border> </DockPanel> </ControlTemplate> </Setter.Value> </Setter> </Trigger> </Style.Triggers> </Style> </Window.Resources> <TextBox Margin="12,69,12,70" Name="txtRecharge" Style="{StaticResource txtboxerrors}"> <TextBox.Text> <Binding Path="Field" Source="{StaticResource recharge}" ValidatesOnDataErrors="True" UpdateSourceTrigger="PropertyChanged"> <Binding.ValidationRules> <ExceptionValidationRule /> </Binding.ValidationRules> </Binding> </TextBox.Text> </TextBox> <Button Height="23" Margin="98,0,0,12" Name="btnRecharge" VerticalAlignment="Bottom" Click="btnRecharge_Click" HorizontalAlignment="Left" Width="75" Style="{StaticResource validButton}">Recharge</Button> some C# : class General : IDataErrorInfo { private string _field; public string this[string columnName] { get { string result = null; if(columnName == "Field") { if(Util.NullOrEmtpyCheck(this._field)) { result = "Field cannot be Empty"; } } return result; } } public string Error { get { return null; } } public string Field { get { return _field; } set { _field = value; } } } So what are suggestion you guys have for me? I mean how would you go about this? how do you do this since the databinding first purpose here is not to load data onto the fields they are just (for now) for data validation. thanks for reading this.

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  • Java conditional operator ?: result type

    - by Wangnick
    I'm a bit puzzled about the conditional operator. Consider the following two lines: Float f1 = false? 1.0f: null; Float f2 = false? 1.0f: false? 1.0f: null; Why does f1 become null and the second statement throws a NullPointerException? Langspec-3.0 para 15.25 sais: Otherwise, the second and third operands are of types S1 and S2 respectively. Let T1 be the type that results from applying boxing conversion to S1, and let T2 be the type that results from applying boxing conversion to S2. The type of the conditional expression is the result of applying capture conversion (§5.1.10) to lub(T1, T2) (§15.12.2.7). So for false?1.0f:null T1 is Float and T2 is the null type. But what is the result of lub(T1,T2)? This para 15.12.2.7 is just a bit too much ... BTW, I'm using 1.6.0_18 on Windows. PS: I know that Float f2 = false? (Float) 1.0f: false? (Float) 1.0f: null; doesn't throw NPE.

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  • Binding type variables that only occur in assertions

    - by Giuseppe Maggiore
    Hi! I find it extremely difficult to describe my problem, so here goes nothing: I have a bunch of assertions on the type of a function. These assertions rely on a type variable that is not used for any parameter of the function, but is only used for internal bindings. Whenever I use this function it does not compile because, of course, the compiler has no information from which to guess what type to bind my type variable. Here is the code: {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables, TypeOperators, TypeSynonymInstances #-} class C a a' where convert :: a -> a' class F a b where apply :: a -> b class S s a where select :: s -> a data CInt = CInt Int instance S (Int,String) Int where select (i,_) = i instance F Int CInt where apply = CInt f :: forall s a b . (S s a, F a b) => s -> b f s = let v = select s :: a y = apply v :: b in y x :: Int x = f (10,"Pippo") And here is the generated error: FunctorsProblems.hs:21:4: No instances for (F a Int, S (t, [Char]) a) arising from a use of `f' at FunctorsProblems.hs:21:4-17 Possible fix: add an instance declaration for (F a Int, S (t, [Char]) a) In the expression: f (10, "Pippo") In the definition of `x': x = f (10, "Pippo") Failed, modules loaded: none. Prelude>

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  • Type classe, generic memoization

    - by nicolas
    Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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