Question

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?

Answer 1

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.