I am calling a generic method with two different classes as below:
FillDataPointsInOrder<Metrics>(dataPoints.Where(O => O.SortOrder != null).OrderBy(O => O.SortOrder));
FillDataPointsInOrder<Metric>(angieStatsCmp.GetDataColumns());
private void FillDataPointsInOrder<T>(IEnumerable<T> dataPoints)
{
foreach (T dpoint in dataPoints)
{
if (!dpoint.IsPhone)
FillDrp(this.EmailDrp, dpoint.Name, dpoint.MetricId.ToString(), dpoint.VName);
if (dpoint.IsPhone && this.IsPhoneShop)
FillDrp(this.PhoneDrp, dpoint.Name, dpoint.MetricId.ToString(), dpoint.VName);
}
}
in "FillDataPointsInOrder" method I am getting compile errors :
'T' does not contain a definition for 'IsPhone' and no extension method 'IsPhone' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?)
Same errors for Name , MetricId and VName properties.
Not sure why T is not able to access properties of Metrics and Metric.
If I remove the code from generic method and write it directly in foreach over dataPoints it is working fine.
Can somebody advise what is wrong here?
FillDataPointsInOrder only knows it will be called with a T. T could actually be string, int or anything.
If you want to call properties on T, you will have to use a where constraint.
But in this case it looks like your method does not even need to be generic.
If both Metric and Metrics share a base class or an interface that has the properties you need:
interface IMetric {
bool IsPhone {get; }
}
you could just have:
private void FillDataPointsInOrder(IEnumerable<IMetric> dataPoints)
Note that IEnumerable is covariant, so if Metric is a IMetric, IENumerable<Metric> is a IEnumerable<IMetric>
You need to at least tell the compiler something about T if you want to do that. Do you have an interface that has members like IsPhone, Name, MetricId, etc. that your classes implement?
If so you can add a 'where' constraint to your class definition:
public class Something<T> where T : ISomethingElse
...where ISomethingElse is the interface that implements IsPhone.
Related
I'm trying to define Callbackdefinitions to make it easier to work with many callbacks in my Node.js project.
My database.ts file looks like that:
export default class Database {
//Export the enums
public static LoadObjectResponse = LoadObjectResponse;
//Export Callback definitions
public static loadObjectCallback: (resultCode: Database.LoadObjectResponse) => void;//ERROR
...
}
enum LoadObjectResponse {
ERROR_ON_LOADING, //"Error on Loading Object.",
OBJECT_NOT_FOUND //"Object not found."
}
So I want a loadObjectCallback defined, that says that the parameter has to be of the enum Type LoadObjectResponse. But when I try to do it like that, the compiler always gives the error
Cannot find namespace "Database"
I don't understand why it gives me the error, the variable itself is in the definition of Database, why doesn't it work?
It gives me the same error when I try to use it in Classfunction definitions:
public static loadObject(MongoModel, searchObject, callback: Database.LoadObjectResponse) {//ERROR namespace Database not found
Again Error:
Cannot find namespace "Database"
Inside of functions in the Database class calling
Database.LoadObjectResponse
works flawlessly, why doesn't it work in variable definitions?
Cannot find namespace "Database"
This is a common learning curve issue. You need to understand and be comfortable with the intutive concept of declaration spaces : https://basarat.gitbook.io/typescript/project/declarationspaces
Things are distinct in the type declaration space or in the variable declaration space.
In your case public static LoadObjectResponse is a variable hence cannot be used as a type (error on annotation usage : Database.LoadObjectResponse).
Fix
Please don't treat a class as a namespace. The file is a module.
export class Database {
//Export Callback definitions
public static loadObjectCallback: (resultCode: LoadObjectResponse) => void;//ERROR
}
export enum LoadObjectResponse {
ERROR_ON_LOADING, //"Error on Loading Object.",
OBJECT_NOT_FOUND //"Object not found."
}
Also beware of export default : https://basarat.gitbook.io/typescript/main-1/defaultisbad
It's because Database.LoadObjectResponse is a property and not a type. You can't use properties as types.
To make this work, change it to use the type of the property:
static loadObjectCallback: (resultCode: typeof Database.LoadObjectResponse) => void;
Or refer directly to the enum type of LoadObjectResponse:
static loadObjectCallback: (resultCode: LoadObjectResponse) => void
I have just come across an interesting gotcha where optional arguments on an interface and the implementing class can conflict.
I found this out the hard way (school boy error) whilst experimenting. You cannot spot it in the debugger and I assumed it was me messing up the dependency injection.
I'm guessing this is so an alternative interface can give a differing view on what default behaviour should be?
Is there a compiler warning or style cop rule to help point this out?
public interface MyInterface
{
MyStuff Get(bool eagerLoad = true); //this overrules the implementation.
}
public class MyClass : MyInterface
{
public MyStuff Get(bool eagerLoad = false) //will still be true
{
//stuff
}
}
Remember default arguments are a compile-time feature. The compiler picks up the default argument based on the static type of the reference in question and inserts the appropriate default argument. I.e. if you reference is of the interface type you get one behavior but if the reference is of the class type you get the other in your case.
I have searched this issue but with no luck. Here we go.
Suppose I have an interface:
interface IQueryRepository<T> where T : class
and I want to bind any requests for:
IQueryRepository<IClient>
to:
ConcreteQueryRepository<Client>
I've tried the obvious:
Bind<IGenericQueryRepository<IClient>>().To<ConcreteQueryRepository<Client>>()
But I get an error:
ConcreteQueryRepository<Client> cannot be used as type parameter 'TImplementation' in
the generic type or method 'Ninject.Syntax.IBindingToSyntax<T>.To<TImplementation>()'
There is no implicit reference conversion from 'ConcreteQueryRepository<Client>'
to 'IGenericQueryRepository<IClient>'
But I don't understand why since GenericQueryRepository implements IGenericQueryRepository and Client implements IClient.
I would like Ninject to give me a concrete generic repository where T is Client. I want this to avoid using concrete types in the code.
Can it be done?
This has to do with Covariance and Contravariance.
In your question you mentioned the following:
... GenericQueryRepository implements IGenericQueryRepository and Client implements IClient.
Let's make it simpler by using fruits: Fruit implements IFruit. We'll also create a Tree class.
public interface IFruit { }
public class Fruit : IFruit { }
public class Tree<T> where T : IFruit { }
Tree<IFruit> tree = new Tree<Fruit>() // error
This will reproduce the same kind of error you're experiencing. Why? Simple.
Though Fruit implements IFruit, an Fruit Tree doesn't implement a IFruit Tree. There is no cast possible between the Fruit Tree and the IFruit Tree, although you would expect it. They are both Trees, but with a different type parameter. The fact that their type parameters are related to each other, doesn't matter.
In other words: there is no cast possible between the Fruit Tree and the IFruit Tree, because their type parameters don't match.
In general, when casting with generics, make sure their type parameters match. However, there are a few exceptional cases. See Variance in Generic Interfaces.
In your case, you could fix it by using IClient as type parameter for the GenericQueryRepository class. Doing this will allow casting because the type parameters match. But I don't know your application architecture, so this fix might be inapplicable in your case.
EDIT: To make it easier to understand, copy paste the code below and see what the compiler says.
interface IFruit { }
class Fruit : IFruit { }
interface ITree<T> where T : IFruit { }
class Tree<T> : ITree<T> where T : IFruit { }
class Program
{
static void Main(string[] args)
{
ITree<Fruit> test1 = new Tree<Fruit>(); // compiles: type parameters match
ITree<IFruit> test2 = new Tree<Fruit>(); // fails: type parameters don't match
ITree<Fruit> test3 = new Tree<IFruit>(); // fails: type parameters don't match
ITree<IFruit> test4 = new Tree<IFruit>(); // compiles: type parameters match
IEnumerable<IFruit> test5 = new List<Fruit>(); // compiles: this is one of the exceptional cases
}
}
That should clear things up about what is and what is not possible.
I've had the same problem when trying to bind a Dapper query to an interface type, thinking about it, it seems to make sense that Dapper can't instantiate an Interface type.
The interface is only a contract and does not know about how to instantiate a concrete implementation of it.
Dapper needs a type that is concrete implementation of the interface type otherwise Dapper would also have to know which concrete implementation of the interface to instantiate, and in that case Dapper would behave like a DI container which, indeed, it isn't.
To start: This is also for REST deserialiaztion, so a custom XmlSerializer is out of the question.
I have a hjierarchy of classes that need to be serializable and deserializable from an "Envelope". It has an arrayelement named "Items" that can contain subclasses of the abstract "Item".
[XmlArray("Items")]
public Item [] Items { get; set; }
Now I need to add XmlArrayItem, but the number is not "fixed". We use so far reflection to find all subclasses with a KnownTypeProvider so it is easy to extend the assembly with new subtypes. I dont really want to hardcode all items here.
The class is defined accordingly:
[XmlRoot]
[KnownType("GetKnownTypes")]
public class Envelope {
but it does not help.
Changing Items to:
[XmlArray("Items")]
[XmlArrayItem(typeof(Item))]
public Item [] Items { get; set; }
results in:
{"The type
xxx.Adjustment
was not expected. Use the XmlInclude
or SoapInclude attribute to specify
types that are not known statically."}
when tyrying to serialize.
Anyone an idea how I can use XmlInclude to point to a known type provider?
The KnownTypesAttribute does not work for XmlSerializer. It's only used by a DataContractSerializer. I'm quite sure that you can exchange the serializer in WCF, because I have done that for the DataContractSerializer. But if that's not an option, you have to implement IXmlSerializable yourself and handle type lookup there.
Before disqualifying this solution: You just have to implement IXmlSerializable just for a special class which replaces Item[]. Everything else can be handled by the default serializer.
According to: http://social.msdn.microsoft.com/Forums/en-US/asmxandxml/thread/83181d16-a048-44e5-b675-a0e8ef82f5b7/
you can use different XmlSerializer constructor:
new XmlSerializer(typeof(Base), new Type[] { typeof(Derived1), ..});
Instead of enumerating all derived classes in the base definition like this:
[System.Xml.Serialization.XmlInclude(typeof(Derived1))]
[System.Xml.Serialization.XmlInclude(typeof(Derived2))]
[System.Xml.Serialization.XmlInclude(typeof(DerivedN))]
I think you should be able to use your KnownTypeProvider to fill the array in the XmlSerializer's constructor.
I am running into a problem when trying to implicitly convert one of my dynamic types. There are two assemblies with definitions similar to the following:
Configuration.dll:
public class ConfigurationValue : DynamicObject
{
public ConfigurationValue(string val)
{
//...
}
//...
public static implicit operator string(ConfigurationValue val)
{
return val.ToString();
}
}
There is another class in this dll called Configuration with a member variable called Instance (to make the class singleton). This variable holds the ConfigurationValue instances in a dictionary and is of type dynamic. This allows me to do this following:
Server.dll:
//...
if (Configuration.Instance.SecurityLevel != "Insecure")
{
//...
}
Assuming that SecurityLevel is in the dictionary.
This if statement appears verbatim in my code and always fails with the following error:
{"Operator '!=' cannot be applied to operands of type 'System.Dynamic.DynamicObject' and 'string'"}
Previously, when these two classes were in the same assembly, this code worked fine. Can anyone tell me what I'm doing wrong here?
Thanks,
Max
Solved the problem, a little embarrassing actually, I forgot to change the container class for ConfigurationValue (e.g. the type of Configuration.Instance) from internal to public when I moved it to the new assembly, so of course the type couldn't be resolved and the implicit conversion was not found
Try
var SecurityLevel = new ConfigurationValue("Insecure");