Recent questions tagged Generics

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generics - Why are supertrait bounds other than the first not recognized on an associated type?

This snippet is valid in Rust 1.26.1: use std::ops::AddAssign; trait Trait where for<'a> Self: ... being overlooked. What is going here? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - F# explicit member constraints: The type variable ^T could not be generalized because it would escape its scope

I'm attempting to use explicit member constraints in F#. The documentation says "F# supports the complete set of ... not allowed to 'escape'. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - Java List vs ArrayList

As a C++ oldtimer I have managed to solve my problem but I can not wrap my head around the ... WHY? Compiler error: Cannot instantiate See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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594 views

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generics - Unable to create a polymorphic type because the trait cannot be made into an object

I've got this simplified Rust code: use std::io::Result; pub trait PacketBuffer {} pub trait DnsRecordData { fn ... I'd very much appreciate it. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - Type inference not working when passing map function

First of all; thank you for taking the time to read my question. If there is any more ... ArrayHandler state.pausablestopwatch action} See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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528 views

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generics - Map of heterogeneous functions in Typescript

I want to create a registry of different functions in Typescript. For example I have several ... fontsize=14&hidenavigation=1&theme=dark See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - How to cast a list of inheriting objects to a collection of objects in Java?

I've a collection type: Collection<A> collecA And I've a list in my object: List<B> listB Where B ... since Collection is implemented by List. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - Cannot use Java 8 method with lambda arguments without specifying type arguments

I made a method with type arguments, returning a generic type using these type arguments, and taking Function ... type arguments? Thanks! See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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570 views

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generics - Java if ternary operator and Collections.emptyList()

Could you please explain why with the first return type the code can't be compiled? The message is : Type ... singletonList(someVariable); } } } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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542 views

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generics - Mixing nested type parameters and wildcards in Java

Why does trying to compile public class GenericsFail { public static void main(String[] args) { accept(new HashMap ... s not nested inside List. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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534 views

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generics - Moving from direct_to_template to new TemplateView in Django

Looking to update my project to the latest version of django and have found that generic views have changed quite ... that into these new views? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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493 views

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generics - How can I refer to the class type a interface is implementing in Java?

I came to a problem with interfaces in a program I'm making. I want to create a interface which have one of ... Is there another way to do so? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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generics - ClassCast error: Java 7 vs Java 8

Is this a bug or feature? The following code runs fine in Java 7 but throws an exception in Java 8: The last ... (build 25.5-b02, mixed mode) See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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528 views

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generics - Varargs to ArrayList problem in Java

I don't understand why the following does not work: public void doSomething(int... args){ List<Integer> ... the arraylist. Whats going on? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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482 views

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generics - Serializing Map<Date, String> with Jackson

I want to serialize a Map with Jackson. The Date should be serialized as a timestamp, like all my other dates ... jackson? Thanks for any hint. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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455 views

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generics - Useful operations on free arrows

We know free monads are useful, and packages like Operational make it easy to define new monads by only caring ... would be the useful ones. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1.0k views

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generics - Way to make Java parent class method return object of child class

Is there any elegant way to make Java method located within parent class return object of child class, when this ... of this.getClass() class. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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548 views

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generics - Why following types are reifiable& non-reifiable in java?

In computing, reification has come to mean an explicit representation of a type-that is, run-time type information. ... ,7,8 as non-reifiable? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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505 views

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generics - Why are not all type information erased in Java at runtime?

My obviously wrong understanding of Java Generics was up to now, that Type Erasure removes all type information ... explanation for this effect? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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556 views

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generics - How do I setup multiple type bounds in Scala?

I want to be able to declare something like this: trait Narrowable[A] extends Iterable[A] { def narrow[B <: ... A and AnyRef. Is this possible? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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581 views

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generics - What is out keyword in kotlin

I am not able to understand and I couldn't find the meaning of out keyword in kotlin. You can check ... . It would be really appreciated. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1.5k views

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generics - Kotlin: How to work with List casts: Unchecked Cast: kotlin.collections.List<Kotlin.Any?> to kotlin.colletions.List<Waypoint>

I want to write a function that returns every item in a List that is not the first or the last item ... this function without this warning? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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520 views

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generics - C#: No implict conversion from Class<Child> to Class<Base>

Following snippet wouldn't compile. With following error: Cannot implicitly convert type 'Container<ChildClass>' to ' ... what is the reason? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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569 views

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generics - How do I unwrap an arbitrary number of nested Option types?

I'm trying to write a trait that will allow me to "unwrap" multiple nested Option<Option<...<T>>>> to a ... method call resolves to `Option<T>` See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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482 views

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generics - Storing different types of elements in a List in Java

I'm trying to develop a general table loader which schema is known at runtime. This requires having a class ... way to implement such class? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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698 views

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generics - Getting T.class despite Java's type-erasure

I'm trying to bind an interface to its implementation as read from a configuration file so that I can feed it ... possible to get T.class? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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518 views

1 answer

generics - Why can't I use a key function that returns a reference when sorting a vector with sort_by_key?

I'm trying to sort a Vec<String> using a key function that returns references to the strings in the vector. ... key type K completely generic? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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413 views

1 answer

generics - Why does java.util.Properties implement Map<Object,Object> and not Map<String,String>

The java.util.Properties class is meant to represent a map where the keys and values are both Strings. This is ... type errors at compile time? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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