generics

问题 Suppose I want to create 2 types of metric : metricA or metricB after transforming another dataset. If a certain condition is met, it'll generate both metricA and B, if condition is not met, generate only metric A. The idea is to write the 2 metrics to 2 different paths (pathA, pathB). The approach I took was to create a Dataset of GeneralMetric and then based on whats inside, write to different paths, but obviously it didn't work as pattern matching inside Dataset wouldn't work val s:

问题 I am trying to customize some ASP.NET Identity Core classes which use Generics. My ApplicationUser class: public class ApplicationUser : IdentityUser<Guid>//, ApplicationUserClaim, ApplicationRole, ApplicationUserLogin> { public ApplicationUser() { } } My ApplicationUserStore class: public class ApplicationUserStore : UserStore<ApplicationUser, ApplicationRole, ApplicationDbContext, Guid> { public ApplicationUserStore(ApplicationDbContext ctx, IdentityErrorDescriber describer = null) : base

问题 I am creating a typed interface defintion and I want to restrict the possible values for the type parameter to a set of classes. These classes are existing already and are not under my control. Also, they are not related to each other through the class hierarchy. So, for example, I have three classes A, B, C. My interface is IMyFancyInterface<T> . How can I restrict implementors of this interface and make sure that T is either A, B, or C only? Thanks a lot. Cheers, Martin 回答1: If A , B and C

问题 I'm using mixins/traits with TypeScript using a subclass factory pattern as described at https://mariusschulz.com/blog/mixin-classes-in-typescript. The trait in question is called Identifiable , which imparts an id property to a class that should express the Identifiable trait. When I attempt to use the trait with another, non-generic trait ( Nameable ) in a certain order, compilation fails. class Empty {} type ctor<T = Empty> = new(...args: any[]) => T; function Nameable<T extends ctor =

问题 Lets say that I have classes which derive from List<T> : public class StringList : List<String> {} public class NameList : StringList {} public class IntList : List<int> {} Now I have a generic method which expects type List<T> : public static Method<T>() { ... } How can I determine the type of elements contained in a list in this method, i.e. how to get the generic argument type in a derived class? For base class I can call typeof(T>.GetGenericArguments() , but for derived class it returns

问题 Lets say that I have classes which derive from List<T> : public class StringList : List<String> {} public class NameList : StringList {} public class IntList : List<int> {} Now I have a generic method which expects type List<T> : public static Method<T>() { ... } How can I determine the type of elements contained in a list in this method, i.e. how to get the generic argument type in a derived class? For base class I can call typeof(T>.GetGenericArguments() , but for derived class it returns

问题 I have a class "Branch". Either classes "Dictionary" and "Link" which I want to use as < T> here. @Entity public class Branch<T> { ... @OneToMany(mappedBy = "branch", orphanRemoval = true, cascade = CascadeType.ALL) private List<T> entities = new ArrayList<>(); } It throws a Runtime Exception: org.hibernate.AnnotationException: Property by.ipps.accounting.model.Branch.branches has an unbound type and no explicit target entity. Resolve this Generic usage issue or set an explicit target

问题 I'm having issues with understanding how matching types in generic functions work in swift. I do not understand why my code is not compiling. This is what I have: enum LoadingState<T> { case idle case loading case failed(Error) case loaded(T) } private func updateInternal(_ state: Int) { print("=int") } private func updateInternal(_ state: String) { print("=string") } private func update<T>(_ state: LoadingState<T>) { switch state { case .loaded(let viewModel): updateInternal(viewModel)

问题 With Typescript 3.5.1, I can't seem to get the type of values to compile. For the following: type foo = 'a' | 'b' const x: Map<foo, {[key: string]: string}> = new Map([ ['a', {'ok': 'so'}], ['b', {'nah': 'right'}] ]) tsc barfs up const x: Map<foo, { [key: string]: string; }> Type 'Map<"a" | "b", { 'ok': string; 'nah'?: undefined; } | { 'nah': string; 'ok'?: undefined; }>' is not assignable to type 'Map<foo, { [key: string]: string; }>'. Type '{ 'ok': string; 'nah'?: undefined; } | { 'nah':

问题 I had a problem with generic traits in a larger context and try to size it down to this smaller problem. I want to have following function: fn count<I, S, T>(pattern: T, item:I) -> usize where I: Atom, S: Iterator<Item = I> T: Atoms<I, S>, { pattern.atoms().filter(|i| i == &item).count() } The function should be passed two arguments: pattern:Atoms<...> which has a factory method atoms returning an iterator of atoms item:Atom which is the item that should be counted in the iterator of atoms