Search Results

Search found 1008 results on 41 pages for 'generics'.

Page 27/41 | < Previous Page | 23 24 25 26 27 28 29 30 31 32 33 34  | Next Page >

• understanding syb boilerplate elimination

  - by Pradeep

  In the example given in http://web.archive.org/web/20080622204226/http://www.cs.vu.nl/boilerplate/ -- Increase salary by percentage increase :: Float -> Company -> Company increase k = everywhere (mkT (incS k)) -- "interesting" code for increase incS :: Float -> Salary -> Salary incS k (S s) = S (s * (1+k)) how come increase function compiles without binding anything for the first Company mentioned in its type signature. Is it something like assigning to a partial function? Why is it done like that?

  Read the article

• [VB.Net] Typecasting generic parameters.

  - by CFP

  Hello world! Using the following code: Function GetSetting(Of T)(ByVal SettingName As String, ByRef DefaultVal As T) As T Return If(Configuration.ContainsKey(SettingName), CType(Configuration(SettingName), T), DefaultVal) End Function Yields the following error: Value of type 'String' cannot be converted to 'T'. Any way I could specify that in all cases, the conversion will indeed be possible (I'm basically getting integers, booleans, doubles and strings). Thanks!

  Read the article

• is there some lightweight tecnique for adding type safety to identifier properties?

  - by shoren

  After using C++ I got used to the concept of Identifier which can be used with a class for the type, provides type safety and has no runtime overhead (the actual size is the size of the primitive). I want to do something like that, so I will not make mistakes like: personDao.find(book.getId());//I want compilation to fail personDao.find(book.getOwnerId());//I want compilation to succeed Possible solutuions that I don't like: For every entity have an entity id class wrapping the id primitive. I don't like the code bloat. Create a generic Identifier class. Code like this will not compile: void foo(Identifier book); void foo(Identifier person); Does anyone know of a better way? Is there a library with a utility such as this? Is implementing this an overkill? And the best of all, can this be done in Java without the object overhead like in C++?

  Read the article

• When using a repository is it possible for a type to return a Func that the repository uses to test for existing entities?

  - by Scott Rickman

  For example given a Factory with a method public static T Save<T>(T item) where T : Base, new() { /* item.Id == Guid.Empty therefore item is new */ if (item.Id == Guid.Empty && repository.GetAll<T>(t => t.Name == item.Name)) { throw new Exception("Name is not unique"); } } how do I create a property of Base (say MustNotAlreadyExist) so that I can change the method above to public static T Save<T>(T item) where T : Base, new() { /* item.Id == Guid.Empty therefore item is new */ if (item.Id == Guid.Empty && repository.GetAll<T>(t.MustNotAlreadyExist)) { throw new Exception("Name is not unique"); } } public class Base { ... public virtual Expression<Func<T, bool>> MustNotAlreadyExist() { return (b => b.Name == name); /* <- this clearly doesn't work */ } } and then how can I override MustNotAlreadyExist in Account : Base public class Account : Base { ... public override Expression<Func<T, bool>> MustNotAlreadyExist() { return (b => b.Name == name && b.AccountCode == accountCode); /* <- this doesn't work */ } ... }

  Read the article

• Interface with generic parameters- can't get it to compile

  - by user997112

  I have an interface like so: public interface MyInterface<E extends Something1> { public void meth1(MyClass1<E> x); } and I have a subclass whose superclass implements the above interface: public class MyClass2<E extends Something1> extends Superclass{ public MyClass2(){ } public void meth1(MyClass1 x) { // TODO Auto-generated method stub } } superclass: public abstract class Superclass<E extends Something1> implements MyInterface{ MyClass1<E> x; protected E y; public Superclass(){ } } the problem is that the parameter for meth1() is supposed to be generic. If I do MyClass1 it doesn't like it and the only way I can get it to compile is by leaving out generic parameters- which feels wrong. What's going wrong?

  Read the article

• removing items from a generic List<t>

  - by frosty

  I have the following method, I wish to remove items from my collection that match the product Id. Seems fairly straight forward, but i get an exception. Basically my collection is getting out of sync. So what is the best way to remove an item from a collection. public void RemoveOrderItem(Model.Order currentOrder, int productId) { foreach (var orderItem in currentOrder.OrderItems) { if (orderItem.Product.Id == productId) { currentOrder.OrderItems.Remove(orderItem); } } } Exception Details: System.InvalidOperationException: Collection was modified; enumeration operation may not execute

  Read the article

• C# specifying generic delegate type param at runtime

  - by smerlin

  following setup, i have several generic functions, and i need to choose the type and the function identified by two strings at runtime. my first try looked like this: public static class FOOBAR { public delegate void MyDelegateType(int param); public static void foo<T>(int param){...} public static void bar<T>(int param){...} public static void someMethod(string methodstr, string typestr) { MyDelegateType mydel; Type mytype; switch(typestr) { case "int": mytype = typeof(int); break; case "double": mytype = typeof(double); break; default: throw new InvalidTypeException(typestr); } switch(methodstr) { case "foo": mydel = foo<mytype>; //error break; case "bar": mydel = bar<mytype>; //error break; default: throw new InvalidTypeException(methodstr); } for(int i=0; i<1000; ++i) mydel(i); } } since this didnt work, i nested those switchs (a methodstr switch inside the typestr switch or viceversa), but that solution is really ugly and unmaintainable. The number of types is pretty much fixed, but the number of functions like foo or bar will increase by high numbers, so i dont want nested switchs. So how can i make this working without using nested switchs ?

  Read the article

• Unit test approach for generic classes/methods

  - by Greg

  Hi, What's the recommended way to cover off unit testing of generic classes/methods? For example (referring to my example code below). Would it be a case of have 2 or 3 times the tests to cover testing the methods with a few different types of TKey, TNode classes? Or is just one class enough? public class TopologyBase<TKey, TNode, TRelationship> where TNode : NodeBase<TKey>, new() where TRelationship : RelationshipBase<TKey>, new() { // Properties public Dictionary<TKey, NodeBase<TKey>> Nodes { get; private set; } public List<RelationshipBase<TKey>> Relationships { get; private set; } // Constructors protected TopologyBase() { Nodes = new Dictionary<TKey, NodeBase<TKey>>(); Relationships = new List<RelationshipBase<TKey>>(); } // Methods public TNode CreateNode(TKey key) { var node = new TNode {Key = key}; Nodes.Add(node.Key, node); return node; } public void CreateRelationship(NodeBase<TKey> parent, NodeBase<TKey> child) { . . .

  Read the article

• How to make TObjectDictionary.Values accessible as property?

  - by Holgerwa

  I have an object like this: TMyObj = class private FObjList: TObjectDictionary <integer, TMyObject>; public constructor Create; destructor Destroy; // How to access Values correctly? Something similar to this not working code property Values: TValueCollection read FObjList.Values write FObjList.Values; end; var MyObj: TMyObj; To access the values of FObjList, I'd like to write: for tmpObject in MyObj.Values do ... How do I need to declare the property "Values" so that MyObj.Values behaves exactly as if I would access MyObj.FObjList.Values?

  Read the article

• Wouldn't it be nice to have a type variable referring to the class's instance.

  - by user93197

  I often have a pattern like this: class VectorBase<SubClass, Element> where SubClass : VectorBase<SubClass, Element>, new() where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(); result.data = newData; return result; } } class VectorInt : VectorBase<VectorInt, Int32> { } class MyInt : Addable<MyInt> { int data; public MyInt(int data) { this.data = data; } public MyInt add(MyInt t) { return new MyInt(data + t.data); } } interface Addable<T> { T add(T t); } But I would rather just have: class VectorBase2<Element> where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(data); return result; } } class VectorInt2 : VectorBase2<Int32> { } Why not make the subclass type available to all classes? Is this technically impossible?

  Read the article

• implementing the generic interface

  - by user845405

  Could any one help me on implementing the generic interface for this class. I want to be able to use the below Cache class methods through an interface. Thank you for the help!. public class CacheStore { private Dictionary<string, object> _cache; private object _sync; public CacheStore() { _cache = new Dictionary<string, object>(); _sync = new object(); } public bool Exists<T>(string key) where T : class { Type type = typeof(T); lock (_sync) { return _cache.ContainsKey(type.Name + key); } } public bool Exists<T>() where T : class { Type type = typeof(T); lock (_sync) { return _cache.ContainsKey(type.Name); } } public T Get<T>(string key) where T : class { Type type = typeof(T); lock (_sync) { if (_cache.ContainsKey(key + type.Name) == false) throw new ApplicationException(String.Format("An object with key '{0}' does not exists", key)); lock (_sync) { return (T)_cache[key + type.Name]; } } } public void Add<T>(string key, T value) { Type type = typeof(T); if (value.GetType() != type) throw new ApplicationException(String.Format("The type of value passed to cache {0} does not match the cache type {1} for key {2}", value.GetType().FullName, type.FullName, key)); lock (_sync) { if (_cache.ContainsKey(key + type.Name)) throw new ApplicationException(String.Format("An object with key '{0}' already exists", key)); lock (_sync) { _cache.Add(key + type.Name, value); } } } } Could any one help me on implementing the generic interface for this class. I want to be able to use the below Cache class methods through an interface.

  Read the article

• C#: Func<T, TResult> for generic methods

  - by SDReyes

  It is possible to create a Func object what references a generic method? like the LINQ OrderBy: public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>( this IEnumerable<TSource> source, Func<TSource, TKey> keySelector )

  Read the article

• F# compilation error: Unexpected type application

  - by Jim Burger

  In F#, given the following class: type Foo() = member this.Bar<'t> (arg0:string) = ignore() Why does the following compile: let f = new Foo() f.Bar<Int32> "string" While the following won't compile: let f = new Foo() "string" |> f.Bar<Int32> //The compiler returns the error: "Unexpected type application"

  Read the article

• C++ Generic List Assignment

  - by S73417H

  I've clearly been stuck in Java land for too long... Is it possible to do the C++ equivalent of the following Java code: // Method List<Bar> getBars() { return new LinkedList<Bar>(); } // Assignment statement. List<Foo> stuff = getBars(); Where Foo is a sub-class of Bar. So in C++.... std::list<Bar> & getBars() { std::list<Bar> bars; return bars; } std::list<Foo> stuff = getBars(); Hope that makes sense....

  Read the article

• Passing the Class<T> in java of a generic list?

  - by Rob Stevenson-Leggett

  I have a method for reading JSON from a service, I'm using Gson to do my serialization and have written the following method using type parameters. public T getDeserializedJSON(Class<T> aClass,String url) { Reader r = getJSONDataAsReader(url); Gson gson = new Gson(); return gson.fromJson(r, aClass); } I'm consuming json which returns just an array of a type e.g. [ { "prop":"value" } { "prop":"value" } ] I have a java class which maps to this object let's call it MyClass. However to use my method I need to do this: RestClient<ArrayList<MyClass>> restClient = new RestClient<ArrayList<MyClass>>(); ArrayList<MyClass> results = restClient.getDeserializedJSON(ArrayList<MyClass>.class, url); However, I can't figure out the syntax to do it. Passing just ArrayList.class doesn't work. So is there a way I can get rid of the Class parameter or how do I get the class of the ArrayList of MyClass?

  Read the article

• Getting the type of a parametrized class parameter?

  - by GuidoMB

  I have the following class public class MyClass<T> { public Class<T> getDomainClass() { GET THE CLASS OF T } } I've googled this problem and all the answers I could find told me to use getGenericSuperClass(), but the problem of this method is that I must have a second class that extends MyClass and I don't want to do this. What I need is to get the parametrized type of a concrete class?

  Read the article

• How to find the class object of Java generic type?

  - by Samuel Yung

  Assume I have a generic type P which is an Enum, that is <P extends Enum<P>>, and I want to get the Enum value from a string, for example: String foo = "foo"; P fooEnum = Enum.valueOf(P.class, foo); This will get a compile error because P.class is invalid. So what can I do in order to make the above code work?

  Read the article

• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

  Read the article

• Get derived class type from a base's class static method

  - by Marco Bettiolo

  Hi, i would like to get the type of the derived class from a static method of its base class. How can this be accomplished? Thanks! class BaseClass { static void Ping () { Type t = this.GetType(); // should be DerivedClass, but it is not possible with a static method } } class DerivedClass : BaseClass {} // somewhere in the code DerivedClass.Ping();

  Read the article

• How could I know if an object is derived from a specific generic class?

  - by Edison Chuang

  Suppose that I have an object then how could I know if the object is derived from a specific generic class. For example: public class GenericClass<T> { } public bool IsDeriveFrom(object o) { return o.GetType().IsSubclassOf(typeof(GenericClass)); //will throw exception here } please notice that the code above will throw an exception. The type of the generic class cannot be retrieved directly because there is no type for a generic class without a type parameter provided.

  Read the article

• PropertyInfo.GetValue() - how do you index into a generic parameter using reflection in C#?

  - by flesh

  This (shortened) code.. for (int i = 0; i < count; i++) { object obj = propertyInfo.GetValue(Tcurrent, new object[] { i }); } .. is throwing a 'TargetParameterCountException : Parameter count mismatch' exception. The underlying type of 'propertyInfo' is a Collection of some T. 'count' is the number of items in the collection. I need to iterate through the collection and perform an operation on obj. Advice appreciated.

  Read the article

• Why can I derived from a templated/generic class based on that type in C# / C++

  - by stusmith

  Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

  Read the article

• Can I pass a non-generic type where a generic type is expected?

  - by Water Cooler v2

  I want to define a set of classes that collect and persist data. I want to call them either on-demand basis, or in a chain-of-responsibility fashion, as the caller pleases. To support the chaining, I have declared my interface like so: interface IDataManager<T, K> { T GetData(K args); void WriteData(Stream stream); void WriteData(T data, Stream stream); IDataCollectionPolicy Policy; IDataManager<T, K> NextDataManager; } But the T's and K's for each concrete types will be different. If I give it like this: IDataManager<T, K> NextDataManager; I assume that the calling code will only be able to chain types that have the same T's and K's. Is there a way I can have it chain any type of IDataManager? One thing that occurs to me is to have IDataManager inherit from a non-generic IDataManager like so: interface IDataManager { } interface IDataManager<T, K>: IDataManager { T GetData(K args); void WriteData(Stream stream); void WriteData(T data, Stream stream); IDataCollectionPolicy Policy; IDataManager NextDataManager; } Is this going to work?

  Read the article

• Reflection for Class of generic parameter in Java?

  - by hatboysam

  Imagine the following scenario: class MyClass extends OtherClass<String>{ String myName; //Whatever } class OtherClass<T> { T myfield; } And I am analyzing MyClass using reflection specifically (MyClass.class).getDeclaredFields(), in this case I will get the following fields (and Types, using getType() of the Field): myName --> String myField --> T I want to get the actual Type for T, which is known at runtime due to the explicit "String" in the extends notation, how do I go about getting the non-genetic type of myField?

  Read the article

• Any way to make a generic List where I can add a type AND a subtype?

  - by user383178

  I understand why I cannot do the following: private class Parent { }; private class Child extends Parent { }; private class GrandChild extends Child { }; public void wontCompile(List<? extends Parent> genericList, Child itemToAdd) { genericList.add(itemToAdd); } My question is there ANY practical way to have a typesafe List where you can call add(E) where E is known to be only a Parent or a Child? I vaguely remember some use of the "|" operator as used for wildcard bounds, but I cannot find it in the spec... Thanks!

  Read the article

< Previous Page | 23 24 25 26 27 28 29 30 31 32 33 34  | Next Page >