contravariance Questions
5
Solved
I will start by saying that I am Java developer learning to program in C#. As such I do comparisons of what I know with what I am learning.
I have been playing with C# generics for a few hours no...
Collocate asked 21/3, 2012 at 14:2
2
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Could you please explain using small and simple TypeScript examples what is Variance, Covariance, Contravariance, Bivariance and Invariance?
Goober asked 28/2, 2021 at 14:30
2
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Assume I have interface and class:
public interface ITree {}
public class Tree : ITree {}
As IEnumerable<T> is covariant, the code line below is compiled successfully:
IEnumerable<ITre...
Grassplot asked 5/10, 2012 at 9:32
5
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I have a struct that has inner mutability.
use std::cell::RefCell;
struct MutableInterior {
hide_me: i32,
vec: Vec<i32>,
}
struct Foo {
//although not used in this particular snippet,
/...
Numbers asked 1/4, 2015 at 22:2
6
I am working on a ASP.NET Core 2.2 Web API application with Mediatr.
I have a handler that looks like -
public class MyQueryHandler<T> : IRequestHanlder<MyQuery<T>, IQueryable<...
Audiometer asked 15/8, 2019 at 2:57
1
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I have a function that expects a short lived object. I would expect that I would be able to always pass it a long lived object. But I am getting a strange error when I try to encode that:
type F<...
Hydrokinetic asked 18/8, 2022 at 19:8
5
Solved
Given the followin snippet, i quite dont understand WHY what im going to achieve is not possible:
Interface:
public interface IEntityRepository<out T> : IRepository<IEntity> {
void ...
Paver asked 1/7, 2016 at 7:52
1
Solved
C++20 allows the program to specify concept for template template argument. For example,
#include <concepts>
template <typename T> concept Char = std::same_as<T, char>;
template ...
Lidstone asked 2/8, 2021 at 13:22
6
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I am having trouble understanding the difference between covariance and contravariance.
Drypoint asked 2/2, 2010 at 14:7
2
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Consider the contravariant interface definition with a delegate:
public interface IInterface<in TInput>
{
delegate int Foo(int x);
void Bar(TInput input);
void Baz(TInput input, Foo fo...
Houseline asked 27/2, 2021 at 17:4
0
The following code demonstrates it clearly:
trait Poly1Group[-IUB, +OUB] {
trait Case[-I <: IUB] {
type Out <: OUB // <------------------------------- success
def apply(v: I): Out
...
Recoup asked 28/1, 2021 at 20:20
3
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Consider the following code:
public class Main {
static class Animal {}
static class Dog extends Animal {}
static List<? extends Animal> foo() {
List<Dog> dogs = new ArrayList<...
Hatter asked 4/8, 2020 at 8:31
4
Solved
Can anyone explain the concept of covariance and contravariance in
programming language theory?
Prohibitive asked 22/7, 2009 at 6:49
1
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I want to write a TypeScript method decorator that can only be applied to methods with a certain type of first argument. It's a common pattern in the codebase I'm working in to pass around a reques...
Pah asked 30/1, 2020 at 18:33
5
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I believe one can define covariance (at least, for objects) as 'the ability to use a value of a narrower (sub) type in place of a value of some wider (super) type', and that contravariance is the e...
Heir asked 15/5, 2012 at 15:27
3
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Today, I read some articles about Covariance, Contravariance (and Invariance) in Java. I read the English and German Wikipedia article, and some other blog posts and articles from IBM.
But I'm sti...
Insectile asked 12/12, 2011 at 21:44
2
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I never truly understood generics in Java, so it seems to be the case with Kotlin. Consider the following code snippet (it's a contrived example):
class AnyComparator: Comparator<Any> {
ove...
Swearingen asked 1/7, 2017 at 14:18
2
public class Flea : Animals {...}
var fleas = new Dictionary<int, Flea>();
public IReadOnlyDictionary<string, Animal> Animals => fleas.ToDictionary(pair => pair.Key, pair => ...
Billingsley asked 14/6, 2019 at 7:33
1
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In the Nomicon's section about subtyping, it says contravariance is available for a function pointer type. However, I can't find any good examples of this. I tried to code a struct with a function ...
Ronnaronnholm asked 25/3, 2019 at 19:9
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In Eric Lippert's blog posts about covariance and contravariance or variance for short, and in books such as C# in a Nutshell, it is stated that :
If you’re defining a generic delegate type, it...
Shillong asked 28/2, 2019 at 15:56
1
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When learning more about the standard event model in .NET, I found that before introducing generics in C#, the method that will handle an event is represented by this delegate type:
//
// Summary:...
Eviaevict asked 27/2, 2019 at 14:3
2
Solved
I can't understand why the following C# code doesn't compile.
As you can see, I have a static generic method Something with an IEnumerable<T> parameter (and T is constrained to be an IA inte...
Circumpolar asked 7/11, 2018 at 8:30
7
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The C# spec states that an argument type cannot be both covariant and contravariant at the same time.
This is apparent when creating a covariant or contravariant interface you decorate your type p...
Fillip asked 24/12, 2010 at 20:22
3
Solved
One of the rules that Liskov Substitution Principle imposes on method signature in derived class is:
Contravariance of method arguments in the subtype.
If I understood correctly, it is saying ...
Preemie asked 31/10, 2016 at 10:24
4
Solved
What does the statement mean?
From here
ref and out parameters in C# and
cannot be marked as variant.
1) Does it mean that the following can not be done.
public class SomeClass<R, A>:...
Hennessey asked 20/5, 2010 at 17:33
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