通用集合碰撞 [英] Generic collection collision

问题描述

  public interface IFoo 
 {
 
 
 $ b $ public class Foo：IFoo {} 
 
 public class Bar：IFoo {} 
 
 public class CollectionOf< T> ：列出< IFoo> 
 {
 
} 
 
 public class Bars：CollectionOf< Bar> 
 {
 
} 
 
 public class Test 
 {
 public void Test（）
 {
 CollectionOf<的IFoo> bars = new Bars（）; 
 
 
 
 
 $ b 
编译器抱怨实例化。酒吧是IFoos的集合。是否这是协变/逆变问题之一？
解决方案
解决方案，如果有的话将取决于它不是什么为你工作。我可以通过两种方式让您的示例进行编译，可以使用IEnumerable或将CollectionOf定义为具有out泛型修饰符的接口。无论是哪一种解决方案我都不知道： 
 
 
  public interface IFoo {} 
 
 public class Foo：IFoo {} 
 
 public class Bar：IFoo {} 
 
 public interface CollectionOf< out T> ：IEnumerable< IFoo> {} 
 
 public class Bars：CollectionOf< Bar> {} 
 
 public class Test 
 {
 public void Test（）
 {
 IEnumerable< IFoo> bars1 =新Bars（）; 
 CollectionOf< IFoo> bars2 =新Bars（）; 
} 
} 
  
 
Here's my best attempt to recreate the situation.
public interface IFoo
{

}

public class Foo : IFoo { }

public class Bar : IFoo { }

public class CollectionOf<T> : List<IFoo>
{

}

public class Bars : CollectionOf<Bar>
{

}

public class Test
{
    public void Test()
    {
        CollectionOf<IFoo> bars = new Bars();
    }
}
Compiler complains on the instantiation. Bars is a collection of IFoos. Is this one of those covariance/contravariance issues?
解决方案
The fix, if there is one would depend on what it is that's not working for you.  I can get your example to compile in two ways, either use IEnumerable or define your CollectionOf as an interface with the out generic modifier.  Whether either is a fix for you I don't know:
public interface IFoo { }

public class Foo : IFoo { }

public class Bar : IFoo { }

public interface CollectionOf<out T> : IEnumerable<IFoo> { }

public class Bars : CollectionOf<Bar> { }

public class Test
{
    public void Test()
    {
        IEnumerable<IFoo> bars1 = new Bars();
        CollectionOf<IFoo> bars2 = new Bars();
    }
}


                        
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