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• Type attribute for text_field

  - by Koning Baard XIV

  I have this code: <%= f.text_field :email, :type => "email", :placeholder => "[email protected]" %> So people can enter their email on an iPhone with the email keyboard instead of the ASCII keyboard. However, the output is: <input id="user_email" name="user[email]" placeholder="[email protected]" size="30" type="text" /> which should be: <input id="user_email" name="user[email]" placeholder="[email protected]" size="30" type="email" /> Is there a way to force Rails to use the email type instead of text, or must I use HTML directly? Thanks

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• Type casting in objective-c

  - by Joy

  Hi all, Is there any way how can i convert a nstimeinterval type value to a string type in xcode? Thanks in advance Joy

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• wpf: design time error while writing Nested type in xaml

  - by viky

  I have created a usercontrol which accept type of enum and assign the values of that enum to a ComboBox control in that usercontrol. Very Simple. I am using this user control in DataTemplates. Problem comes when there comes nested type. I assign that using this notation EnumType="{x:Type myNamespace:ParentType + NestedType}" It works fine at runtime. but at design time it throws error saying Could not create an instance of type 'TypeExtension' Why? Due to this I am not able to see my window at design time. Any help?

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• Is there an easy way to check a fundamental type

  - by Dbger

  In < Modern C++ Design ,it introduces a way to check if a type fundamental type by introducing the so called type list. but what if I don't want to include so many loki code and just want a simple function to implement that? What is the simplest way to do that?

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• Java class object from type variable

  - by Alexander Temerev

  Is there a way to get Class object from the type variable in Java generic class? Something like that: public class Bar extends Foo<T> { public Class getParameterClass() { return T.class; // doesn't compile } } This type information is available at compile time and therefore should not be affected by type erasure, so, theoretically, there should be a way to accomplish this. Does it exist?

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• Unboxing to unknown type

  - by Robert

  I'm trying to figure out syntax that supports unboxing an integral type (short/int/long) to its intrinsic type, when the type itself is unknown. Here is a completely contrived example that demonstrates the concept: // Just a simple container that returns values as objects struct DataStruct { public short ShortVale; public int IntValue; public long LongValue; public object GetBoxedShortValue() { return LongValue; } public object GetBoxedIntValue() { return LongValue; } public object GetBoxedLongValue() { return LongValue; } } static void Main( string[] args ) { DataStruct data; // Initialize data - any value will do data.LongValue = data.IntValue = data.ShortVale = 42; DataStruct newData; // This works if you know the type you are expecting! newData.ShortVale = (short)data.GetBoxedShortValue(); newData.IntValue = (int)data.GetBoxedIntValue(); newData.LongValue = (long)data.GetBoxedLongValue(); // But what about when you don't know? newData.ShortVale = data.GetBoxedShortValue(); // error newData.IntValue = data.GetBoxedIntValue(); // error newData.LongValue = data.GetBoxedLongValue(); // error } In each case, the integral types are consistent, so there should be some form of syntax that says "the object contains a simple type of X, return that as X (even though I don't know what X is)". Because the objects ultimately come from the same source, there really can't be a mismatch (short != long). I apologize for the contrived example, it seemed like the best way to demonstrate the syntax. Thanks.

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• Explain ML type inference to a C++ programmer

  - by Tsubasa Gomamoto

  How does ML perform the type inference in the following function definition: let add a b = a + b Is it like C++ templates where no type-checking is performed until the point of template instantiation after which if the type supports the necessary operations, the function works or else a compilation error is thrown ? i.e. for example, the following function template template <typename NumType> NumType add(NumType a, NumType b) { return a + b; } will work for add<int>(23, 11); but won't work for add<ostream>(cout, fout); Is what I am guessing is correct or ML type inference works differently? PS: Sorry for my poor English; it's not my native language.

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• functional dependencies vs type families

  - by mhwombat

  I'm developing a framework for running experiments with artificial life, and I'm trying to use type families instead of functional dependencies. Type families seems to be the preferred approach among Haskellers, but I've run into a situation where functional dependencies seem like a better fit. Am I missing a trick? Here's the design using type families. (This code compiles OK.) {-# LANGUAGE TypeFamilies, FlexibleContexts #-} import Control.Monad.State (StateT) class Agent a where agentId :: a -> String liveALittle :: Universe u => a -> StateT u IO a -- plus other functions class Universe u where type MyAgent u :: * withAgent :: (MyAgent u -> StateT u IO (MyAgent u)) -> String -> StateT u IO () -- plus other functions data SimpleUniverse = SimpleUniverse { mainDir :: FilePath -- plus other fields } defaultWithAgent :: (MyAgent u -> StateT u IO (MyAgent u)) -> String -> StateT u IO () defaultWithAgent = undefined -- stub -- plus default implementations for other functions -- -- In order to use my framework, the user will need to create a typeclass -- that implements the Agent class... -- data Bug = Bug String deriving (Show, Eq) instance Agent Bug where agentId (Bug s) = s liveALittle bug = return bug -- stub -- -- .. and they'll also need to make SimpleUniverse an instance of Universe -- for their agent type. -- instance Universe SimpleUniverse where type MyAgent SimpleUniverse = Bug withAgent = defaultWithAgent -- boilerplate -- plus similar boilerplate for other functions Is there a way to avoid forcing my users to write those last two lines of boilerplate? Compare with the version using fundeps, below, which seems to make things simpler for my users. (The use of UndecideableInstances may be a red flag.) (This code also compiles OK.) {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances #-} import Control.Monad.State (StateT) class Agent a where agentId :: a -> String liveALittle :: Universe u a => a -> StateT u IO a -- plus other functions class Universe u a | u -> a where withAgent :: Agent a => (a -> StateT u IO a) -> String -> StateT u IO () -- plus other functions data SimpleUniverse = SimpleUniverse { mainDir :: FilePath -- plus other fields } instance Universe SimpleUniverse a where withAgent = undefined -- stub -- plus implementations for other functions -- -- In order to use my framework, the user will need to create a typeclass -- that implements the Agent class... -- data Bug = Bug String deriving (Show, Eq) instance Agent Bug where agentId (Bug s) = s liveALittle bug = return bug -- stub -- -- And now my users only have to write stuff like... -- u :: SimpleUniverse u = SimpleUniverse "mydir"

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• Cannot initialize non-const reference from convertible type

  - by Julien L.

  Hi, I cannot initialize a non-const reference to type T1 from a convertible type T2. However, I can with a const reference. long l; const long long &const_ref = l; // fine long long &ref = l; // error: invalid initialization of reference of // type 'long long int&' from expression of type // 'long int' Most problems I encountered were related to r-values that cannot be assigned to a non-const reference. This is not the case here -- can someone explain? Thanks.

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• GHC.Generics and Type Families

  - by jberryman

  This is a question related to my module here, and is simplified a bit. It's also related to this previous question, in which I oversimplified my problem and didn't get the answer I was looking for. I hope this isn't too specific, and please change the title if you can think if a better one. Background My module uses a concurrent chan, split into a read side and write side. I use a special class with an associated type synonym to support polymorphic channel "joins": {-# LANGUAGE TypeFamilies #-} class Sources s where type Joined s newJoinedChan :: IO (s, Messages (Joined s)) -- NOT EXPORTED --output and input sides of channel: data Messages a -- NOT EXPORTED data Mailbox a instance Sources (Mailbox a) where type Joined (Mailbox a) = a newJoinedChan = undefined instance (Sources a, Sources b)=> Sources (a,b) where type Joined (a,b) = (Joined a, Joined b) newJoinedChan = undefined -- and so on for tuples of 3,4,5... The code above allows us to do this kind of thing: example = do (mb , msgsA) <- newJoinedChan ((mb1, mb2), msgsB) <- newJoinedChan --say that: msgsA, msgsB :: Messages (Int,Int) --and: mb :: Mailbox (Int,Int) -- mb1,mb2 :: Mailbox Int We have a recursive action called a Behavior that we can run on the messages we pull out of the "read" end of the channel: newtype Behavior a = Behavior (a -> IO (Behavior a)) runBehaviorOn :: Behavior a -> Messages a -> IO () -- NOT EXPORTED This would allow us to run a Behavior (Int,Int) on either of msgsA or msgsB, where in the second case both Ints in the tuple it receives actually came through separate Mailboxes. This is all tied together for the user in the exposed spawn function spawn :: (Sources s) => Behavior (Joined s) -> IO s ...which calls newJoinedChan and runBehaviorOn, and returns the input Sources. What I'd like to do I'd like users to be able to create a Behavior of arbitrary product type (not just tuples) , so for instance we could run a Behavior (Pair Int Int) on the example Messages above. I'd like to do this with GHC.Generics while still having a polymorphic Sources, but can't manage to make it work. spawn :: (Sources s, Generic (Joined s), Rep (Joined s) ~ ??) => Behavior (Joined s) -> IO s The parts of the above example that are actually exposed in the API are the fst of the newJoinedChan action, and Behaviors, so an acceptable solution can modify one or all of runBehaviorOn or the snd of newJoinedChan. I'll also be extending the API above to support sums (not implemented yet) like Behavior (Either a b) so I hoped GHC.Generics would work for me. Questions Is there a way I can extend the API above to support arbitrary Generic a=> Behavior a? If not using GHC's Generics, are there other ways I can get the API I want with minimal end-user pain (i.e. they just have to add a deriving clause to their type)?

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• How to check the type of a Parameter in an Expression Tree (similar to 'is' keyword)

  - by Callum Rogers

  How do I check the type of a Parameter in an Expression Tree (and get the Expression Tree equivalent of a bool if it the right type)? If it were normal code, I would do this: if(myObj is int) I see there is a Expression.Convert method but this converts the object instead of just checking its type. EDIT: I found the answer, you use a Expression.TypeIs

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• c++ floating point to integer type conversions

  - by moala

  What are the different techniques for a floating point type to an integer type conversion, in c++?

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• In C#, how do I check if a type is a subtype OR the type of an object?

  - by Daniel T.

  To check if a type is a subclass of another type in C#, it's easy: typeof (SubClass).IsSubclassOf(BaseClass); // returns true However, this will fail: typeof (BaseClass).IsSubclassOf(BaseClass); // returns false Is there any way to check whether a type is either a subclass OR of the base class itself, without using an OR operator or using an extension method?

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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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• C++ auto function return type implementation [trailing-return-type]

  - by aaa

  hello. Is there macro, something like BOOST_AUTO, which would allow to emulate automatic return type deduction of function in C++? I mean something like trailing-return-type, http://en.wikipedia.org/wiki/C%2B%2B0x#Alternative_function_syntax thank you

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• To convert PyBytesObject type to PyUnicodeObject type in python3

  - by sam

  How to convert pyunicodeobject type to pybytesobject type? Example: function(PyBytesObject* byteobj){ ....operation.. } PyUnicodeObject* Uniobj; function((PyBytesObject*) Uniobj); got a bus error as a result.

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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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• SQL Server: Declaring variable type based on a column type

  - by Bernard Dy

  In Oracle's PL-SQL, you can declare a variable and define its type based on a table column: declare var1 table.column%TYPE; Is it possible to do something similar in MS SQL Server? I searched but could not find a duplicate for this question. If there is one, please let me know and I'll refer to it and delete this.

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