The as operator is more efficient because it actually returns the cast value if the cast can be made successfully. The is operator returns only a Boolean value. It can therefore be used when we just want to determine an object’s type but do not have to actually cast it.
Use the is operator to verify the type before performing a cast.
Use the as operator and test for null before referencing the variable.
Use the as operator to test an incompatible type.
Use the as operator with a value type. Note the implicit conversion to int? in the method body.
example–class SafeCasting
{
class Animal
{
public void Eat() { Console.WriteLine(“Eating.”); }
public override string ToString()
{
return “I am an animal.”;
}
}
class Mammal : Animal { }
class Giraffe : Mammal { }
class SuperNova { }
static void Main()
{
SafeCasting app = new SafeCasting();
// Use the is operator to verify the type. before performing a cast.
Giraffe g = new Giraffe();
app.UseIsOperator(g);
// Use the as operator and test for null before referencing the variable.
app.UseAsOperator(g);
// Use the as operator to test an incompatible type.
SuperNova sn = new SuperNova();
app.UseAsOperator(sn);
// Use the as operator with a value type.
// Note the implicit conversion to int? in
// the method body.
int i = 5;
app.UseAsWithNullable(i);
double d = 9.78654;
app.UseAsWithNullable(d);
// Keep the console window open in debug mode.
System.Console.WriteLine(“Press any key to exit.”);
System.Console.ReadKey();
}
void UseIsOperator(Animal a)
{
if (a is Mammal)
{
Mammal m = (Mammal)a;
m.Eat();
}
}
void UseAsOperator(object o)
{
Mammal m = o as Mammal;
if (m != null)
{
Console.WriteLine(m.ToString());
}
else
{
Console.WriteLine(“{0} is not a Mammal”, o.GetType().Name);
}
}
void UseAsWithNullable(System.ValueType val)
{
int? j = val as int?;
if (j != null)
{
Console.WriteLine(j);
}
else
{
Console.WriteLine(“Could not convert ” + val.ToString());
}
}
}