Recipe 4.3: Inheriting from Literal Values

Perl6 Object Oriented Cookbook (v0.2.1)
Section 4: Inheritance

Recipe 4.3: Inheriting from Literal Values

Last Updated: Sep 8, 2003
Status: Draft

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Problem:

You want your class to inherit from a literal value.

Solution:

Just do it:

class WombatString is "wombat";  # note the quotes!

class ZeroButTrue is 0 {         # OO version of "0 but true"
    as boolean 1;
}

Discussion:

In the second example above, we have declared a class, ZeroButTrue, that inherits from the literal value 0. Then we've declared a transformation (See Section 5) which specifies that when this object is evaluated in boolean context, it should return the literal value 1, e.g. "true".

This can be an extremely powerful way to quickly make classes that are treated as literal (constant) values in almost all situations, but that have extra methods or transformations that the original value didn't.

When inheriting from a literal value, you are inheriting from an instance of whatever builtin type that literal value represents. See Section 6 to learn what builtin types exist in perl, and how to subclass those builtin types.

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