Type test operators

Type test operators

The as, is, and is! operators are handy for checking types atruntime.

The result of obj is T is true if obj implements the interfacespecified by T. For example, obj is Object is always true.

Use the as operator to cast an object to a particular type. Ingeneral, you should use it as a shorthand for an is test on an objectfollowed by an expression using that object. For example, consider thefollowing code:

if (emp is Person) {
  // Type check
  emp.firstName = 'Bob';
}

You can make the code shorter using the as operator:

(emp as Person).firstName = 'Bob';

Note: The code isn’t equivalent. If emp is null or not a Person, the first example (with is) does nothing; the second (with as) throws an exception.