Is it okay to name the ":isa" attribute for single inheritance?

[yuki-kimoto]

Is it okay to name the ":isa" attribute for single inheritance?

https://github.com/Ovid/Cor/blob/master/rfc/classes.md#422-inheritance

class Customer :isa(Person 3.14) :version(v2.1.0) {
    field $customer_id :param;

    method name :overrides () {
        my $name = $self->next::method();
        $name .= " (#$customer_id)";
        return $name;
    }
}

The reason I ask this question is Perl has already "isa" operator.

$object isa Foo

"isa" operator check @isa in both single inheritance and multiple inheritance.

And if the role is implemented internally using multiple inheritance, the result of "isa" operator maybe be true.

class MyClass :isa(Parent) :does(Role1, Role2) {

}

my $object = MyClass->new;

if ($object isa Role1) {
  # What result? I think it maybe true.
}

people may ask. "Why does the isa operator return true even though the ":isa" attribute is not specified?"

[HaraldJoerg]

In short: It is ok to name the ":isa" attribute for single inheritance.

Both the attribute and the operator can be read like "is a" in English to give the correct understanding. A customer is a person - makes sense. "is a" expects singular terms on both sides.

In your example if ($object isa Role1) the code will not return true: Role1 is not a class, and not added to the @ISA of MyClass. With Corinna this could be caught as a syntax error because Corinna roles identify themselves at compile time. Applied to a role implemented with Moose::Role, isa Role simply returns false.

A corresponding does operator in Perl does not yet exist because Perl core does not have roles (yet).

[yuki-kimoto]

Thanks.

In your example if ($object isa Role1) the code will not return true: Role1 is not a class

Role1 is not a class, and not added to the @isa of MyClass.

I understood now.