Creating custom exceptions

In the previous sections, we have seen that exceptions in Perl 6 use the object-oriented approach, which, in particular, helps to distinguish between different exceptions in the CATCH block.

In this section, we will create a custom exception that is integrated into the Perl 6 system as smoothly as any other built-in classes in the X:: namespace. If you do not have any special requirements, create your custom exception classes in the same namespace.

For example, let us create a Lift class together with the X::Lift::Overload exception, which will be triggered when too many people enter the lift:

class Lift {
    class X::Lift::Overload is Exception {
        method message {
            'Too many people!'
        }
    }

    has $.capacity = 5;
    has $!people;
    method enter(Int $n = 1) {
        $!people += $n;
        X::Lift::Overload.new.throw if $!people > $!capacity;
    }
}

We don't need the exception class outside the Lift class, so it is better to restrict...