非空接口代码契约实现 - 默认（T）VS抛NotImplementedException [英] Implementation of non-void interface Code Contracts - default(T) vs throw NotImplementedException

问题描述

这可能是风格大多是问题，但定义非void接口成员，代码合同时，哪种方法是最好的：

This may be mostly a question of style but when defining code contracts for non-void interface members, which approach is best:

接口：

[ContractClass(typeof(IFooContract))]
public interface IFoo
{
    object Bar();
}

合同选项1：

Contract option 1:

[ContractClassFor(typeof(IFoo))]
public abstract class IFooContract : IFoo
{
    object IFoo.Bar()
    {
        Contract.Ensures(Contract.Result<object>() != null);
        throw new NotImplementedException();
    }
}

合同选项2：

Contract option 2:

[ContractClassFor(typeof(IFoo))]
public abstract class IFooContract : IFoo
{
    object IFoo.Bar()
    {
        Contract.Ensures(Contract.Result<object>() != null);
        return default(T);
    }
}

大多数我见过的文献倾向于选择2，但我觉得选择1比较好，因为它是清晰的，这纯粹是关于合同（和选项2，技术上打破它刚刚定义的合同）。

Most of the literature I've seen tend towards option 2 but I feel that option 1 is better as it is clearer that this is purely about the contract (and option 2 is technically breaking the contract it just defined).

是那里有选项2优于选项1的任何方案？

Are there any scenarios where option 2 is preferred over option 1?

推荐答案

抛出异常在语义上更正确的，因为合同类可不再被调用，并在一个看似合理的方式使用;来电者将被停止，并告诉他们的错误。

Throwing an exception is semantically more correct, because the contract class can no longer be invoked and used in a seemingly reasonable way; callers will be stopped and told about their error.

然而， NotImplementedException 似乎并没有被正确的例外抛出：那异常通常标志着一个尚未实现的代码（如方法体）的部分。但非 - 无效合同法的的的实施;它只是不意味着被调用。因此，我宁愿一个出现InvalidOperationException 或引发NotSupportedException 。

However, NotImplementedException does not seem to be the proper exception to throw: That exception usually marks a section of code (such as a method body) that has yet to be implemented. But a non-void contract method has been implemented; it just isn't meant to be called. Thus I would prefer an InvalidOperationException or a NotSupportedException.

（你甚至可以引发自定义异常类型，例如一个 NotMeantToBeCalledException ）

(You could even throw a custom exception type, e.g. a NotMeantToBeCalledException.)

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