我如何安全地投了System.Object的一个`bool`在C＃中？ [英] How do I safely cast a System.Object to a `bool` in C#?

问题描述

我提取一个（非通用，hetrogeneous）集合布尔值。

I am extracting a bool value from a (non-generic, hetrogeneous) collection.

在为运营商可能只引用类型使用，所以这是不可能做到的使用为来尝试一个安全，强制转换为布尔：

The as operator may only be used with reference types, so it is not possible to do use as to try a safe-cast to bool:

// This does not work: "The as operator must be used with a reference type ('bool' is a value type)"
object rawValue = map.GetValue(key);
bool value = rawValue as bool;

有没有类似的事情可以做，所以安全对象转换值类型没有的可能性 InvalidCastException的如果，无论出于何种原因，该值不是一个布尔？

Is there something similar that can be done so safely cast an object to a value type without possibility of an InvalidCastException if, for whatever reason, the value is not a boolean?

推荐答案

有两个选项...略有令人惊讶的表现：

There are two options... with slightly surprising performance:

• 冗余校验：

• Redundant checking:

if (rawValue is bool)
{
    bool x = (bool) rawValue;
    ...
}

使用可空类型：

Using a nullable type:

bool? x = rawValue as bool?;
if (x != null)
{
    ... // use x.Value
}

令人惊讶的是，在<一个href="http://stackoverflow.com/questions/1583050/performance-surprise-with-as-and-nullable-types">performance第二形式的比第一的差很多。

The surprising part is that the performance of the second form is much worse than the first.

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