代码契约是否未能发现 Nullable.HasValue 和 null 之间的明显关系？

发布于 2024-11-26 18:05:48 字数 362 浏览 3 评论 0原文

我正在尝试将代码契约应用于我的代码，但遇到了一个令人困惑的问题。这段代码未能满足合同要求，但除非我真的很厚，否则我希望它能够轻松分析 id 在返回时必须有一个值

if (id == null)
    throw new InvalidOperationException(string.Format("{0} '{1}' 尚无标识", typeof(T).Name,entity));

返回 id.Value；

代码合约错误：需要未经验证：HasValue

原文

I am experimenting with applying Code Contracts to my code and I've hit a perplexing problem.
This code is failing to meet the contract but unless I'm being really thick I would expect it to be able to easily analyse that id must have a value at the point of return

if (id == null)
    throw new InvalidOperationException(string.Format("{0} '{1}' does not yet have an identity", typeof(T).Name, entity));

return id.Value;

Code Contracts error: requires unproven: HasValue

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唯憾梦倾城 2024-12-03 18:05:48

我已经查清了这种行为的真相，这不是 Code Contract 的错。

我在 ILSpy 中打开生成的程序集，这是生成的代码：

public Guid Id
{
    get
    {
        Guid? guid = this.id;
        if (!guid.HasValue)
        {
            throw new InvalidOperationException();
        }
        guid = this.id;
        return guid.Value;
    }
}

实例变量 id 被复制到局部变量，并且该局部变量在条件块之后被重置回其原始值。现在，代码合同显示合同违规错误的原因已经很明显了，但它仍然让我困惑为什么代码要以这种形式重写。我做了更多的实验，并将代码契约从项目中完全删除，很明显这是标准的 C# 编译器行为，但为什么呢？

这个秘密似乎是由于我在最初的问题中不小心遗漏了一个小细节。 id 实例变量被声明为 readonly，这似乎是导致编译器添加临时 guid 变量的原因。

我必须承认我仍然很困惑为什么编译器认为需要这样做以确保 id 的不变性保证，但我会继续挖掘......

I've got to the bottom of this behaviour and it is not Code Contract's fault.

I opened the generated assembly in ILSpy and this is the code that is produced:

public Guid Id
{
    get
    {
        Guid? guid = this.id;
        if (!guid.HasValue)
        {
            throw new InvalidOperationException();
        }
        guid = this.id;
        return guid.Value;
    }
}

The instance variable id is being copied to a local variable and this local variable is being reset back to its original value after the condition block. Now it became obvious why Code Contracts is showing a contract violation error but it still left me confused why the code was being rewritten in this form. I did a little more experimentation and took Code Contracts out of the project altogether and it became apparent that this is standard C# compiler behaviour, but why?

The secret appears to be due to a minor detail that I accidentally omitted from my original question. The id instance variable is declared as readonly and this seems to be responsible for causing the compiler to add the temporary guid variable.

I must admit I'm still confused why the compiler feels it needs to do this to ensure the guarantee of immutability for id but I'll keep digging...

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旧竹 2024-12-03 18:05:48

您可以尝试将该字段复制到本地值并根据该本地值编写语句。证明者可能对字段持保守态度，因为调用可能会改变字段值。

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多孤肩上扛 2024-12-03 18:05:48

它没有看到你的 if throw 检查作为其合同的一部分。请尝试以下操作：

if (id == null)    
  throw new InvalidOperationException(string.Format("{0} '{1}' does not yet have an identity", typeof(T).Name, entity));

Contract.EndContractBlock();

http://msdn.microsoft .com/en-us/library/system.diagnostics.contracts.contract.endcontractblock.aspx

Its not seeing your if throw check as part of its contracts. Try this instead:

if (id == null)    
  throw new InvalidOperationException(string.Format("{0} '{1}' does not yet have an identity", typeof(T).Name, entity));

Contract.EndContractBlock();

http://msdn.microsoft.com/en-us/library/system.diagnostics.contracts.contract.endcontractblock.aspx

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