Covariance and Contravariance FAQ

re: Covariance and Contravariance FAQ

Ganesh — Wed, 03 Oct 2012 15:02:00 GMT

Nice article, I understood the concept now after reading this article

re: Covariance and Contravariance FAQ

Dima Kurguzov — Sun, 08 Apr 2012 01:21:31 GMT

Sorry, string is not a value type, then it is not a boxing.

re: Covariance and Contravariance FAQ

Dima Kurguzov — Sun, 08 Apr 2012 00:27:03 GMT

May be I am not right, but the first lines of code demonstrates the boxing not assigning of a more derived type to an object of a less derived type. Please correct me if I am wrong.

string str = "test";

// An object of a more derived type is assigned to an object of a less derived type.

object obj = str;

re: Covariance and Contravariance FAQ

Rajib Banerjee — Sun, 22 Jan 2012 01:34:02 GMT

Object is less derived whereas any other type derived from object such as int or strings or such are more derived.

re: Covariance and Contravariance FAQ

Mr. Kashif Khan — Fri, 25 Feb 2011 09:15:17 GMT

Rusina i could't understand what does this mean "// An object of a more derived type is assigned to an object of a less derived type."? what u mean more derived type and less derived type? which is more derived type and which is less derived type? i am waiting eagerly for this answer so that i can learn this variance :( pls hlp

re: Covariance and Contravariance FAQ

Mat Heuer — Mon, 18 Oct 2010 00:35:19 GMT

@Alexandra Rusina: I would be glad if out-Parameters could be declared as covariant.

Currently it seems as if out and ref Parameters are both treated invariant.

Consider the bool TryGetValue(TKey key, out TValue value) Methods of IDictionary:

Here the Type 'value' should be declared as covariant.

Currently I work around by switching both Return Values:

TValue TryGetValue(TKey key, out bool isValid)

But using this Signature is not as appealing AND the Parameter Type cannot be derived from a Return Value.

Will this be supported in the foreseeable Future?

re: Covariance and Contravariance FAQ

甜番薯 — Fri, 11 Jun 2010 15:04:10 GMT

I had translate this article to chinese.

我已将此文章翻译成中文：

www.cnblogs.com/.../covariance-and-contravariance-faq.html

re: Covariance and Contravariance FAQ

Alexandra Rusina — Tue, 04 May 2010 04:40:02 GMT

@admg

The problems that C# had prior to version 4.0 due to the lack of variance support in generics are well-described here:

http://msdn.microsoft.com/en-us/library/ms228359%28VS.90%29.aspx

Note that this document is for C# 3.0, because now you should use variance in interfaces instead.

re: Covariance and Contravariance FAQ

Mon, 03 May 2010 07:32:47 GMT

@admg

In c#3.5 your statement would not compile. List<string> implements IEnumerable<string> which can not be cast to IEnumerable<object>. C#4.0 allows you to cast IEnumerable<string> to IEnumerable<object>.

re: Covariance and Contravariance FAQ

admg — Sat, 01 May 2010 23:15:07 GMT

Isnt it just hidden casting?

IEnumerable<Object> objects = (IEnumerable<Object>) new List<String>();