Comments on: Generic Variance in C# 4.0 http://kohari.org/2008/10/28/generic-variance-in-c-40/ Rambling and occasional wisdom from Nate Kohari Tue, 09 Mar 2010 12:47:18 -0500 http://wordpress.org/?v=2.8.4 hourly 1 By: Oidon http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-227 Oidon Tue, 18 Nov 2008 15:18:58 +0000 http://kohari.org/?p=172#comment-227 As far as I understand, variance support is only being added for generic interfaces and delegates. (Actually, version 2.0 of the CLI has always supported this; C# is just catching up now.) Thus, your "class Foo" should not compile. As far as I understand, variance support is only being added for generic interfaces and delegates. (Actually, version 2.0 of the CLI has always supported this; C# is just catching up now.) Thus, your “class Foo” should not compile.

]]> By: Buu Nguyen http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-226 Buu Nguyen Fri, 14 Nov 2008 12:57:23 +0000 http://kohari.org/?p=172#comment-226 >>IList{string} strings = new List{string}(); >>IList{object} objects = strings; In IList, T appears in both output and input positions (i.e. add, T []), therefore IList can't be covariant on T. In Java, this would be possible with wildcards. >>IList{string} strings = new List{string}();
>>IList{object} objects = strings;
In IList, T appears in both output and input positions (i.e. add, T []), therefore IList can’t be covariant on T. In Java, this would be possible with wildcards.

]]> By: Nate Kohari http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-225 Nate Kohari Thu, 06 Nov 2008 14:46:40 +0000 http://kohari.org/?p=172#comment-225 @Sebastian: That's a good point. The list example comes directly from the official explanation of the new features, but I haven't tried it myself in the VS2010 CTP. I'd be interested to know... @Sebastian: That’s a good point. The list example comes directly from the official explanation of the new features, but I haven’t tried it myself in the VS2010 CTP. I’d be interested to know…

]]> By: Sebastian Mueller http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-222 Sebastian Mueller Fri, 31 Oct 2008 08:40:56 +0000 http://kohari.org/?p=172#comment-222 Damn, the comment system removed my brackets - replace {} in the below code with the corresponding brackets If you say that this works: IList{string} strings = new List{string}(); IList{object} objects = strings; how is this goingo to work then: objects.Add(new object()); ? this should work for IList{object} but not for IList{string} ! so I don't think that IList is going to have an "out" type parameter, rather the GetEnumerable method of IList{T} might become IEnumerable{out T} - though I haven't read the spec yet and I don't know if you can actually add the out or in keyword to certain methods/properties to the class parameter. (BTW: That's the way Java Generics do it: out T and in T is like "? extends T" and "? super T") Other than that, great article and thanks for the link! /Sebastian Damn, the comment system removed my brackets – replace {} in the below code with the corresponding brackets

If you say that this works:

IList{string} strings = new List{string}();
IList{object} objects = strings;

how is this goingo to work then:

objects.Add(new object());

?
this should work for IList{object} but not for IList{string} !

so I don’t think that IList is going to have an “out” type parameter, rather the GetEnumerable method of IList{T} might become IEnumerable{out T} – though I haven’t read the spec yet and I don’t know if you can actually add the out or in keyword to certain methods/properties to the class parameter.
(BTW: That’s the way Java Generics do it: out T and in T is like “? extends T” and “? super T”)

Other than that, great article and thanks for the link!

/Sebastian

]]> By: Sebastian Mueller http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-224 Sebastian Mueller Fri, 31 Oct 2008 08:37:57 +0000 http://kohari.org/?p=172#comment-224 If you say that this works: IList strings = new List(); IList objects = strings; how is this goingo to work then: objects.Add(new object()); ? this should work for IList but not for IList ! so I don't think that IList is going to have an "out" type parameter, rather the GetEnumerable method of IList might become IEnumerable - though I haven't read the spec yet and I don't know if you can actually add the out or in keyword to certain methods/properties to the class parameter. (BTW: That's the way Java Generics do it: out T and in T is like "? extends T" and "? super T") Other than that, great article and thanks for the link! /Sebastian If you say that this works:

IList strings = new List();
IList objects = strings;

how is this goingo to work then:

objects.Add(new object());

?
this should work for IList but not for IList !

so I don’t think that IList is going to have an “out” type parameter, rather the GetEnumerable method of IList might become IEnumerable – though I haven’t read the spec yet and I don’t know if you can actually add the out or in keyword to certain methods/properties to the class parameter.
(BTW: That’s the way Java Generics do it: out T and in T is like “? extends T” and “? super T”)

Other than that, great article and thanks for the link!

/Sebastian

]]> By: Reflective Perspective - Chris Alcock » The Morning Brew #212 http://kohari.org/2008/10/28/generic-variance-in-c-40/comment-page-1/#comment-223 Reflective Perspective - Chris Alcock » The Morning Brew #212 Thu, 30 Oct 2008 08:32:25 +0000 http://kohari.org/?p=172#comment-223 [...] Generic Variance in C# 4.0 - Nate Kohari looks at the variance of generic types in C#4 [...] [...] Generic Variance in C# 4.0 – Nate Kohari looks at the variance of generic types in C#4 [...]

]]>