‘for backwards compatibility’ seems a sufficient reason for the type erasure of class generic types – it is needed e.g. to allow you to return an untyped List and pass it to some legacy code. The extension of this to generic methods seems like a tricky sub-case. The JLS snippet from 4.8 (which you quote) … Read more
ArrayList is an implementation of List interface. So all ArrayList instances are List instances but all List instances are not necessarily ArrayList. So when you call this method : public static <T> List<T> inRange(List<T> list, int index, int range) { you cannot assign its result to an ArrayList as you are doing : ArrayList<View> inRange … Read more
Checking if a variable conforms to a typing object To check if string_list conforms to string_list_class, you can use the typeguard type checking library. from typeguard import check_type try: check_type(‘string_list’, string_list, string_list_class) print(“string_list conforms to string_list_class”) except TypeError: print(“string_list does not conform to string_list_class”) Checking the generic type of a typing object To check if … Read more
I banged my head on this for a few hours, but the solution seems obvious in retrospect. First I present the solution, then I compare it to prior approaches. (Tested in Typescript 2.6.2.) // WORKING SOLUTION: union of types with type checks class MustBeThis { method1() { } } class OrThis { method2() { } … Read more
This is deliberate. Static classes try to prevent inappropriate use, so in almost all situations, you can’t use them in situations where you’d normally want an instance of the type… and that includes type arguments. See section “Static classes” of the C# 6 spec for the very limited set of situations in which you can … Read more
The wildcards do not make a lot of sense when you declare local variables, however they are really important when you declare a parameter for a method. Imagine you have a method: int countLegs ( List< ? extends Animal > animals ) { int retVal = 0; for ( Animal cur : animals ) { … Read more
To extend any class public static class Extensions { public static T DoSomething<T>(this T obj) { //… } } To extend a specific generic class public static NeedExtension<T> DoSomething<T>(this NeedExtension<T> obj) { //… }
You want something like partial type parameter inference, which is not currently a feature of TypeScript (see microsoft/TypeScript#26242). Right now you either have to specify all type parameters manually or let the compiler infer all type parameters; there’s no partial inference. As you’ve noticed, generic type parameter defaults do not scratch this itch; a default … Read more
tl;dr You can perform a type assertion only on interface values. So you must convert x to a valid interface type first, any / interface{} in this case: func isInt[T any](x T) (ok bool) { _, ok = any(x).(int) // convert, then assert return } So why does this fail to compile? _, ok = … Read more
json_serializable json_serializable has a several strategies1 to handle generic types as single objects T or List<T> (as of v. 5.0.2+) : Helper Class: JsonConverter Helper Methods: @JsonKey(fromJson:, toJson:) Generic Argument Factories @JsonSerializable(genericArgumentFactories: true) 1 Of which I’m aware. There’s likely other ways to do this. Helper Class: JsonConverter Basic idea: write a custom JsonConverter class … Read more