打桩静态扩展方法似乎犀牛制品工作，除非我投返回变量。为什么？ [英] Stubbing a static extension method seems to work in Rhino Mocks unless I cast the return variable. Why?

问题描述

我能够使用存根犀牛制品的静态扩展方法，但如果我将返回值转换为另一种类型，我得到一个错误。为什么？

 使用Rhino.Mocks; 
 
公共接口INumberGenerator 
 {
双GetDouble（）; 
} 
 
静态类NumberGeneratorExtensionMethods 
 {
公共静态双GetTheDouble（此INumberGenerator输入）
 {
返回input.GetDouble（）; 
} 
 
公共静态十进制GetTheDoubleCastToDecimal（此INumberGenerator输入）
 {
回报（十进制）input.GetDouble（）; 
} 
} 
 
类MockExample 
 {
公共无效TriggerTheError（）
 {
 VAR存根= MockRepository.GenerateStub< INumberGenerator>（）; 
 
 //此工程
 stub.Stub（OBJ => obj.GetTheDouble（））返回（1.2D）。 
 
 //这引发错误
 stub.Stub（OBJ => obj.GetTheDoubleCastToDecimal（））返回（1.2米）。 
} 
} 
  

下面是错误：

System.InvalidOperationException：类型System.Decimal不适用于匹配方法的返回类型'System.Double'INumberGenerator.GetDouble（）;

解决方案

警告：这是一个真正的怀疑比什么都重要

的问题是，你没有的真正的存根扩展方法在所有 - 你删 GetDouble 在这两种情况下。

我没有看过的犀牛制品的代码一段时间，但我的犯罪嫌疑人的那在存根方法基本上是说：

• 准备好上模拟一些调用！


• 调用传递作为参数


• 的委托注意它要求作了

这意味着你有效地这样做：

  canGetDecimal.Stub（纳克=> ng.GetDouble（））返回（1.2D）。 
 canGetDecimal.Stub（NG =>（十进制）ng.GetDouble（））返回（1.2米）。 
  

在这一点上，它会注意到你叫 GetDouble - 但是你要设定的返回值，达120万，这是无效的。

您可以验证这很容易地，一些记录。日志行添加到 GetTheDoubleCastToDecimal ，然后拆出从返回存根通话code>电话：

  Console.WriteLine（以前存根）; 
 VAR stubCall = canGetDecimal.Stub（OBJ => obj.GetTheDoubleCastToDecimal（）; 
 Console.WriteLine（存根后）; 
 stubCall.Return（1.2米）; 
  

我强烈怀疑你会发现，无论你记录加入到扩展方法仍然登录以前存根之间以及存根后 - 这表明扩展方法的不的被嘲笑了。

道德：唐T试图模拟/存根扩展方法他们是不是多态;。他们只是静态方法，这将是相当棘手假冒他们不深的魔法，只有尝试假了真正的多态操作

I am able to stub a static extension method using Rhino Mocks but if I cast the return value to another type, I get an error. Why?

using Rhino.Mocks;

public interface INumberGenerator
{
    double GetDouble();
}

static class NumberGeneratorExtensionMethods
{
    public static double GetTheDouble(this INumberGenerator input)
    {
        return input.GetDouble();
    }

    public static decimal GetTheDoubleCastToDecimal(this INumberGenerator input)
    {
        return (decimal) input.GetDouble();
    }
}

class MockExample
{
    public void TriggerTheError()
    {
        var stub = MockRepository.GenerateStub<INumberGenerator>();

        // This works
        stub.Stub(obj => obj.GetTheDouble()).Return(1.2d);

        // This throws the error
        stub.Stub(obj => obj.GetTheDoubleCastToDecimal()).Return(1.2m);
    }
}

Here is the error:

System.InvalidOperationException : Type 'System.Decimal' doesn't match the return type 'System.Double' for method 'INumberGenerator.GetDouble();'

解决方案

Warning: this is really a suspicion more than anything else

The problem is that you're not really stubbing the extension methods at all - you're stubbing GetDouble in both cases.

I haven't looked at the code for Rhino Mocks for a while, but I suspect that the Stub method is basically saying:

• Get ready for some calls on the mock!
• Call the delegate passed in as an argument
• Note which calls were made

That means you're effectively doing this:

canGetDecimal.Stub(ng => ng.GetDouble()).Return(1.2d);
canGetDecimal.Stub(ng => (decimal) ng.GetDouble()).Return(1.2m);

At that point, it would notice that you called GetDouble - but then you're trying to set the return value to 1.2m, which is invalid.

You could validate this pretty easily, with some logging. Add a log line to GetTheDoubleCastToDecimal and then split out the Stub call from the Return call:

Console.WriteLine("Before Stub");
var stubCall = canGetDecimal.Stub(obj => obj.GetTheDoubleCastToDecimal();
Console.WriteLine("After Stub");
stubCall.Return(1.2m);

I strongly suspect you'll find that whatever logging you add into the extension method is still logged between "Before Stub" and "After Stub" - showing that the extension method isn't being mocked out.

Moral: don't try to mock/stub extension methods. They're not polymorphic; they're just static methods, and it would be pretty tricky to fake them without deep wizardry. Only try to fake out genuinely polymorphic operations.

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