实现具有类型约束的通用接口

本文关键字：接口 约束 类型 实现 | 更新日期: 2023-09-27 18:00:09

我有一个Visual Studio 2008 C#2.0 CF项目，我正在该项目中实现一个通用接口IComparison。可以调用IComparison.Compare方法来进行对指定对象有效的任何类型的比较，所以我不想对其施加类型约束。

public interface IComparison<EXPECTED_PARAM>
{
    Result Compare<RETURNED_PARAM>(RETURNED_PARAM returned);
}

然而，执行工作可以更加具体。在这种情况下，我想说的是，给GreaterThan.Compare的参数可以通过System.IComparable与构造函数中给的EXPECTED_PARAM进行比较。

public class GreaterThan<EXPECTED_PARAM> : IComparison<EXPECTED_PARAM>
{
    private EXPECTED_PARAM expected_;
    public GreaterThan(EXPECTED_PARAM expected)
    {
        expected_ = expected;
    }
    public Result Compare<RETURNED_PARAM>(RETURNED_PARAM returned) 
        where RETURNED_PARAM : IComparable< EXPECTED_PARAM >
    {
        return ((returned == null && expected_ == null) ||
                (returned != null && returned.CompareTo( expected_ ) > 0)) ?
               Result.Fail : Result.Pass;
    }
}

不幸的是，这给了我一个错误：

error CS0460: Constraints for override and explicit interface implementation methods are inherited from the base method, so they cannot be specified directly

我需要做些什么才能对EXPECTED_PARAM对象和RETURNED_PARAM对象进行任意比较？

谢谢，PaulH

实现具有类型约束的通用接口

这个怎么样？

    public interface IComparison<EXPECTED_PARAM, RETURNED_PARAM>
{
    Result Compare(RETURNED_PARAM returned);
}
public class GreaterThan<EXPECTED_PARAM, RETURNED_PARAM> : IComparison<EXPECTED_PARAM, RETURNED_PARAM> where RETURNED_PARAM : IComparable<EXPECTED_PARAM>
{
    private EXPECTED_PARAM expected_;      
    public GreaterThan(EXPECTED_PARAM expected)     
    {         expected_ = expected;     }      
    public Result Compare(RETURNED_PARAM returned)          
    {
        return ((returned == null && expected_ == null) || 
            (returned != null && returned.CompareTo( expected_ ) > 0)) ?                
            Result.Fail : Result.Pass;
    }
}

问题出在继承层次结构上。GreaterThan继承自IComparison<EXPECTED_PARAM>，这意味着您告诉编译器它实现了Compare<EXPECTED_PARAM>，但您希望它实现Compare<RETURNED_PARAM>。您可以放弃界面上的通用约束：

public interface IComparison
{
    Result Compare<RETURNED_PARAM>(RETURNED_PARAM returned)
    where RETURNED_PARAM : IComparable;
}
public class GreaterThan<EXPECTED_PARAM>: IComparison
{
    private EXPECTED_PARAM expected_;
    public GreaterThan(EXPECTED_PARAM expected)
    {
        expected_ = expected;
    }
    public Result Compare<RETURNED_PARAM>(RETURNED_PARAM returned) 
        where RETURNED_PARAM : IComparable
    {
        return ((returned == null && expected_ == null) ||
                (returned != null && returned.CompareTo( expected_ ) > 0)) ?
               Result.Fail : Result.Pass;
    }
}
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