blocks|key|5067497|text|我的猜测是这与迭代器的延迟特性有关。请记住，协定处理将在最终发出的IL上发生，而不是在C#代码上。这意味着您必须考虑为迭代器和lambda表达式等功能生成的代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5067498|如果你反编译这些代码，你会发现"i“实际上不是一个参数。它将是用于实现迭代器的类中的一个变量。因此，代码实际上看起来更像下面这样|5067499|class+IteratorImpl+{
++private+int+i;
++public+bool+MoveNext()+{
++++Contract.Require(i+>0);
++++..
++}
}|code-block|syntax|javascript|5067500|我对契约API不是很熟悉，但我猜生成的代码更难验证。|5067501|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

My guess is this has to do with the delayed nature of iterators. Remember, contract processing will occur on the final emitted IL, not the C# code. This means you have to consider the generated code for features like iterators and lambda expressions.

If you decompile that code you'll find that "i" is not actually a parameter. It will be a variable in the class which is used to implement the iterator. So the code actually looks more like the following

<pre><code>class IteratorImpl {
 private int i;
 public bool MoveNext() {
 Contract.Require(i &gt;0);
 ..
 }
}
</code></pre>

I'm not terribly familiar with the contract API but my guess is the generated code is much harder to verify.

blocks|key|1237479|text|请记住，迭代器只有在枚举之后才会运行，并在后端编译成某种特殊的调味品。如果您想要验证参数，您应该遵循的一般模式是拥有一个包装器函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1237480|static+IEnumerable<int>+Test+(int+i)
{
++++Contract.Requires(i+>+0);
++++return+_Test(i);
}

private+static+IEnumerable<int>+_Test+(int+i)
{
++++for+(int+j+=+0;+j+<+i;+j%2B%2B)
++++++++yield+return+j;
}|code-block|syntax|javascript|1237481|这样，Test()将在被调用时检查参数，然后返回_Test()，这实际上只是返回一个新类。|1237482|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Remember that iterators aren't run until they are enumerated, and are compiled into some special sauce in the back end. The general pattern you should follow if you want to validate parameters, and this probably holds true for contracts, is to have a wrapper function:

<pre><code>static IEnumerable&lt;int&gt; Test (int i)
{
 Contract.Requires(i &gt; 0);
 return _Test(i);
}

private static IEnumerable&lt;int&gt; _Test (int i)
{
 for (int j = 0; j &lt; i; j++)
 yield return j;
}
</code></pre>

That way Test() will do the checking of the parameters when it is called then return _Test(), which actually just returns a new class.

blocks|key|3599312|text|这里有一个关于单元测试、迭代器、延迟执行和你的主题的blog+post。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3599313|延迟执行是这里的问题。|3599314|entityMap|0|LINK|mutability|MUTABLE|url|http://codebetter.com/blogs/kyle.baley/archive/2009/06/02/delayed-execution-with-yield-or-how-to-abdicate-cede-and-relent.aspx^0|Q|9|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Here's a <a href="http://codebetter.com/blogs/kyle.baley/archive/2009/06/02/delayed-execution-with-yield-or-how-to-abdicate-cede-and-relent.aspx" rel="nofollow noreferrer">blog post</a> related to this very subject concerning unit testing, iterators, delayed execution, and you.

Delayed execution is the issue here.

blocks|key|1237509|text|这段代码可以在.NET+4.0的最终版本(刚刚试过)中工作，在这个版本中，代码契约在interators中被支持，但我最近发现它并不总是能正常工作(请阅读更多here)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1237510|entityMap|0|LINK|mutability|MUTABLE|url|http://mokosh.co.uk/post/2010/06/26/net-4-code-contracts-and-iterators/^0|11|J|27|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

This code will work with final version of .NET 4.0 (just tried it) where Code Contracts in interators are supported, but as I found out recently it does not always work properly (read more <a href="http://mokosh.co.uk/post/2010/06/26/net-4-code-contracts-and-iterators/" rel="nofollow noreferrer">here</a>).

blocks|key|1283005|text|这可能是过去CodeContract重写器中的一个问题。但当前版本似乎在您的示例中做得很好。这里没有迭代器/延迟求值等问题。参数i是通过值捕获的，在迭代过程中不会改变。契约应该只在调用Test的开始时检查这一点，而不是在每次迭代期间。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1283006|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

This may have been a problem in the CodeContract rewriter in the past. But the current version seems to do fine on your example. There's no issue here with iterators/delayed evaluation etc. The parameter i is captured by value and won't change during the iteration. Contracts should check this only at the beginning of the call to Test, not during each iteration.

The following code fails on the pre condition. Is this a bug in code contracts?

<pre><code>static class Program
{
 static void Main()
 {
 foreach (var s in Test(3))
 {
 Console.WriteLine(s);
 }
 }

 static IEnumerable&lt;int&gt;Test (int i)
 {
 Contract.Requires(i &gt; 0);
 for (int j = 0; j &lt; i; j++)
 yield return j;
 }
}
</code></pre>

Bug in iterators with code contracts?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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以下代码在前置条件下失败。这是代码契约中的一个bug吗？static class Program{    static void Main()    {        foreach (var s in Test(3))        {            Console.WriteLine(s);        ...

问使用代码契约的迭代器中的Bug？
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问使用代码契约的迭代器中的Bug？EN