C# – How to safely cast a System.Object to a `bool` in C#

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

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;

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

Best Answer

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

  • Redundant checking:

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

  • Using a nullable type:

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

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

In C# 7, you can use pattern matching for this:

if (rawValue is bool value)
{
    // Use value here
}

Note that you still end up with value in scope (but not definitely assigned) after the if statement.

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