generics

问题 Lets say I have the following: case class TestField(value: String) case class TestField2(value: String) implicit class ProductExtensions[T <: Product](val value T) extends AnyVal { def mapTo[R <: Product](implicit tGen: Generic.Aux[T, String :: HNil], rGen: Generic.Aux[R, String :: HNil]: R = ??? } val testField2 = TestField("my value").mapTo[TestField2] // TestField2("my value") Can I "genersize" the mapTo function to work for types other than String without having to specify the type? Note

问题 Lets say I have the following: case class TestField(value: String) case class TestField2(value: String) implicit class ProductExtensions[T <: Product](val value T) extends AnyVal { def mapTo[R <: Product](implicit tGen: Generic.Aux[T, String :: HNil], rGen: Generic.Aux[R, String :: HNil]: R = ??? } val testField2 = TestField("my value").mapTo[TestField2] // TestField2("my value") Can I "genersize" the mapTo function to work for types other than String without having to specify the type? Note

问题 What's the best way to call a generic method when the type parameter isn't known at compile time, but instead is obtained dynamically at runtime? Consider the following sample code - inside the Example() method, what's the most concise way to invoke GenericMethod<T>() using the Type stored in the myType variable? public class Sample { public void Example(string typeName) { Type myType = FindType(typeName); // What goes here to call GenericMethod<T>()? GenericMethod<myType>(); // This doesn't

问题 What's the best way to call a generic method when the type parameter isn't known at compile time, but instead is obtained dynamically at runtime? Consider the following sample code - inside the Example() method, what's the most concise way to invoke GenericMethod<T>() using the Type stored in the myType variable? public class Sample { public void Example(string typeName) { Type myType = FindType(typeName); // What goes here to call GenericMethod<T>()? GenericMethod<myType>(); // This doesn't

问题 I am trying to create a class that processes comparables. I boiled down to the simplest code that gives an error when I try to instantiate the class. I get a couple of compile warnings (unchecked cast) but when I run this program it throws a classcast exception. I did look at some of the other questions on this topic but didnt come across something useful. public class GD<Item extends Comparable<Item>> { private Item[] data; private final int MAX_SIZE = 200; public GD() { data = (Item[]) new

问题 here is some sample code: trait A trait B extends A def test[T <: A](): T = { new B {} } but I get an compile error: type mismatch; found : B required: T new B {} how to make it working ? ( but without doing asInstanceOf[T] at the end ) thanks! 回答1: The signature of your method def test[T <: A](): T promises that for any type T that is a subtype of A you return a value of this type T . And then you returned a value of type B . You violated the signature (there are many subtypes of A , not

问题 here is some sample code: trait A trait B extends A def test[T <: A](): T = { new B {} } but I get an compile error: type mismatch; found : B required: T new B {} how to make it working ? ( but without doing asInstanceOf[T] at the end ) thanks! 回答1: The signature of your method def test[T <: A](): T promises that for any type T that is a subtype of A you return a value of this type T . And then you returned a value of type B . You violated the signature (there are many subtypes of A , not

问题 The following fails as per the error message quoted in the comment. It has been boiled down to the bare minimum, so the code below has no apparent practical value. I'm just trying to get a handle on the truly bizarre (in my opinion) error message. The reason I want to declare the array as [P] and not [S] is for the usual run-time polymorphism of the array contents. protocol P { func sp() } struct S: P { func sp() {} } extension Array where Element: P { func am() {} } func t() { let goodA = [S

问题 I have problem as above. My code: public abstract class BaseFactory<T> where T: class { protected static dbModelContainer context = new dbModelContainer(); public static int UpdateDataBase_static() { return context.SaveChanges(); } } and my question is how can I call BaseFactory.UpdateDataBase_static(); instead of: BaseFactory<SomeClass>.UpdateDataBase_static(); Any ideas? 回答1: You can't, because there is no such method. The closest is to have a non-generic base that the generic class

问题 I have problem as above. My code: public abstract class BaseFactory<T> where T: class { protected static dbModelContainer context = new dbModelContainer(); public static int UpdateDataBase_static() { return context.SaveChanges(); } } and my question is how can I call BaseFactory.UpdateDataBase_static(); instead of: BaseFactory<SomeClass>.UpdateDataBase_static(); Any ideas? 回答1: You can't, because there is no such method. The closest is to have a non-generic base that the generic class