盒装的比较值类型 [英] Comparing boxed value types

问题描述

今天，我偶然发现了一个有趣的错误，我写。我有一组可通过一般的setter方法​​来设置属性。这些特性可以是值类型或引用类型。

Today I stumbled upon an interesting bug I wrote. I have a set of properties which can be set through a general setter. These properties can be value types or reference types.

public void SetValue( TEnum property, object value )
{
    if ( _properties[ property ] != value )
    {
        // Only come here when the new value is different.
    }
}

在写这个方法，我发现了一个单元测试条件始终是值类型如此。它没有多久我要弄清楚这是由于装箱/拆箱。它没有多久我要么调整代码如下：

When writing a unit test for this method I found out the condition is always true for value types. It didn't take me long to figure out this is due to boxing/unboxing. It didn't take me long either to adjust the code to the following:

public void SetValue( TEnum property, object value )
{
    if ( !_properties[ property ].Equals( value ) )
    {
        // Only come here when the new value is different.
    }
}

的事情是我不能完全满足于此解。我想保持一个简单的参考比较，除非该值是盒装。

The thing is I'm not entirely satisfied with this solution. I'd like to keep a simple reference comparison, unless the value is boxed.

目前的解决方案我想到的只是调用等于（ ）的盒装值。做的盒装检查值似乎有点矫枉过正。难道没有更简单的方法？

The current solution I am thinking of is only calling Equals() for boxed values. Doing a check for a boxed values seems a bit overkill. Isn't there an easier way?

推荐答案

如果你需要，当你处理一个值类型，那么你不同的行为再显然将需要进行某种形式的测试。你并不需要的盒装的值类型明确的检查，因为所有的值类型将被装箱**由于参数被类型为对象

If you need different behaviour when you're dealing with a value-type then you're obviously going to need to perform some kind of test. You don't need an explicit check for boxed value-types, since all value-types will be boxed** due to the parameter being typed as object.

此代码应符合您所陈述的标准：如果值是一个（盒装）值类型，然后调用多态等于方法，否则使用 == 来测试引用相等。

This code should meet your stated criteria: If value is a (boxed) value-type then call the polymorphic Equals method, otherwise use == to test for reference equality.

public void SetValue(TEnum property, object value)
{
    bool equal = ((value != null) && value.GetType().IsValueType)
                     ? value.Equals(_properties[property])
                     : (value == _properties[property]);

    if (!equal)
    {
        // Only come here when the new value is different.
    }
}

（**是的，我知道可空< T> 是一个值类型有自己的特殊规则有关装箱和拆箱，但是这几乎是无关紧要这里）

( ** And, yes, I know that Nullable<T> is a value-type with its own special rules relating to boxing and unboxing, but that's pretty much irrelevant here.)

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