Use oo::configurable in tcl9.0

Question

I am playing with configure in new version tcl9.0, it works, but I have the question: how to make class both configurable and abstract? I tried to do like this:

oo::abstract create Simulator {
        mixin oo::configurable
        property Name -set {
            error "Not implemented"
        }
        variable Name
}

But it raises the error that property is not known. Thank you in advance!

Answer 1

You need to do:

oo::configurable create Simulator {
    self mixin -append oo::abstract
    property Name -set {
        error "Not implemented"
    }
    variable Name
}

This is because oo::configurable does cunning things to add property to the set of configuration commands, and that means it needs to be asserted prior to oo::define being called (yes, classes just hand that off in their constructor); adding it during the call would mean that only the next time oo::define is called would it be impacted.

By contrast, oo::singleton is very simple; it currently just makes create and new be non-exported methods on the class concerned directly (but not its subclasses) and doesn't alter the definition command context. That makes it simple enough to work as a mixin. We use self mixin -append because we may add other mixins to classes, and want to affect the class object itself.