bounded-types

How can I determine if one Enum value is the successor of another?

由 ╄→尐↘猪︶ㄣ 提交于 2020-05-28 20:49:10
问题 I'm trying to write a function that tells me whether one Enum is the successor of another. Here was my first attempt: isSuccessorOf x y = x == succ y Looks reasonable. Let's try it: λ> isSuccessorOf 3 2 True λ> isSuccessorOf 1 5 False λ> isSuccessorOf 3 (maxBound :: Int) *** Exception: Prelude.Enum.succ{Int}: tried to take `succ' of maxBound Whoops. That should have been False . Let's make sure we don't try to do succ maxBound : isSuccessorOf x y = y /= maxBound && x == succ y Let's try it

Understanding bounded generics in java. What is the point?

由 瘦欲@ 提交于 2020-02-13 05:27:16
问题 I am trying to understand bounded types and not quite grasping the point of them. There is an example of bounded generics on which provides this use case: public class NaturalNumber<T extends Integer> { private T n; public NaturalNumber(T n) { this.n = n; } public boolean isEven() { return n.intValue() % 2 == 0; } // ... } If you are going to restrict the classes that can be the parameterized type, why not just forget the parameterization all together and have: public class NaturalNumber {

Understanding bounded generics in java. What is the point?

由 混江龙づ霸主 提交于 2020-02-13 05:27:14
问题 I am trying to understand bounded types and not quite grasping the point of them. There is an example of bounded generics on which provides this use case: public class NaturalNumber<T extends Integer> { private T n; public NaturalNumber(T n) { this.n = n; } public boolean isEven() { return n.intValue() % 2 == 0; } // ... } If you are going to restrict the classes that can be the parameterized type, why not just forget the parameterization all together and have: public class NaturalNumber {

Cast to generic type (T) gives “unchecked cast” warning

由 杀马特。学长 韩版系。学妹 提交于 2019-12-23 11:14:10
问题 I got a small problem here regarding generics bounded type with lists. Please help out! Model.java public class Model { } ClassA.java public class ClassA<T extends Model> { private List<T> models; public ClassA() { models.add((T) new Model()); } } It gives me an unchecked cast from Model to T warning on this line: models.add((T) new Model()); I understand I'm getting this warning because all I can safely cast from a sub class into a super class but not the other way round. Is there any way to

Android Room: Is it possible to use bounded type parameters in an entity?

由 大兔子大兔子 提交于 2019-12-13 02:56:22
问题 I am currently combining Mike Penz Fastadapter with Android Room. The expandable model class needs to be implemented like this: public class MyClass<Parent extends IItem & IExpandable, SubItem extends IItem & ISubItem> extends AbstractExpandableItem<MyClass<Parent, SubItem>, MyClass.ViewHolder, SubItem> { I want to use the model also as a room entity. The first problem was easy to solve - I created a custom version of AbstractExpandableItem where the fields would be annoteted with @Ignore

How to create many bounded types without duplicating code in Haskell?

由 孤街浪徒 提交于 2019-12-08 04:05:49
问题 For a project, I’ve created a type based on Int which throws an error whenever the program tries to use a value beyond limits ([0..127] in my case). The code below does this and it works for me. Is it possible in Haskell to create a second bounded type (say [0..255] for example) without duplicating this code ? Thanks for your answers {-# LANGUAGE GeneralizedNewtypeDeriving #-} module Minitel.Type.MNatural (MNat, mnat, fromMNat) where -- | The MNat type. The constructor is hidden. newtype MNat

In Java type arguments, does <? extends E> mean strictly subtypes only? or would E also suffice?

由 白昼怎懂夜的黑 提交于 2019-12-06 23:47:10
问题 In Java type arguments, does mean strictly subtypes only? or would E also suffice? 回答1: Yes, super and extends gives inclusive lower and upper bounds respectively. Here's a quote from Angelika Langer's Generics FAQ: What is a bounded wildcard? A wildcard with an upper bound looks like ? extends Type and stands for the family of all types that are subtypes of Type , type Type being included . Type is called the upper bound . A wildcard with a lower bound looks like ? super Type and stands for

In Java type arguments, does <? extends E> mean strictly subtypes only? or would E also suffice?

由 血红的双手。 提交于 2019-12-05 03:43:12
In Java type arguments, does mean strictly subtypes only? or would E also suffice? Yes, super and extends gives inclusive lower and upper bounds respectively. Here's a quote from Angelika Langer's Generics FAQ : What is a bounded wildcard? A wildcard with an upper bound looks like ? extends Type and stands for the family of all types that are subtypes of Type , type Type being included . Type is called the upper bound . A wildcard with a lower bound looks like ? super Type and stands for the family of all types that are supertypes of Type , type Type being included . Type is called the lower

Why are the bounds of type parameters ignored when using existential types in Scala?

由 本秂侑毒 提交于 2019-12-01 07:01:37
问题 What I mean is this: scala> class Bounded[T <: String](val t: T) defined class Bounded scala> val b: Bounded[_] = new Bounded("some string") b: Bounded[_] = Bounded@2b0a141e scala> b.t res0: Any = some string Why does res0 have type Any and not String? It sure could know that b.t is at least a String. Writing val b: Bounded[_ <: String] = new Bounded("some string") works, but it is redundant with respect to the declaration of the class itself. 回答1: First, I have edited the question title. You

Difference between Bounded Type parameter and Upper Bound Wildcard

由 微笑、不失礼 提交于 2019-11-29 09:18:45
I know that there was a similar question already posted, although I think mine is somewhat different... Suppose you have two methods: // Bounded type parameter private static <T extends Number> void processList(List<T> someList) { } // Upper bound wildcard private static void processList2(List<? extends Number> someList) { // ... } As far as I know, both methods accepts arguments, that are List of type Number or List of subtype of Number . But what's the difference between the two methods after all? CKing There are several differences between the two syntaxes during compile time : With the
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