AppleScript: The Definitive Guide, 2nd Edition

Inheritance

Script objects may be linked into a chain of inheritance . One script object inherits from another if the second script is the parent of the first. Then, suppose an attempt is made to access a top-level entity of the first script object (using the special syntax described in "Accessing Top-Level Entities," earlier in this chapter). If the script object has no such top-level entity, the attempt is passed along to its parent to see whether it has such a top-level entity.

It turns out that every script object has a parent property. This property is set for you if you don't set it (and so there is always an inheritance chain, even though you might not be aware of this). To link two script objects explicitly into a chain of inheritance, initialize the parent property of one to point to the other.

Tip

The parent property may be set only through initialization (that is, through a script property declaration). You cannot use copy or set to set it.

In this example, we explicitly arrange two script objects, mommy and baby, into an inheritance chain (by initializing baby's parent property). We can then tell baby to execute a handler that it doesn't have, but which mommy does have. Here we go:

script mommy
    on talk( )
        display dialog "How do you do?"
    end talk
end script
script baby
    property parent : mommy
end script
baby's talk( ) -- How do you do?

In that example, we told the child from outside to execute a handler that it doesn't have but the parent does. The child can also tell itself ...