oo::class , a built-in Tcl command, is the class of all classes in TclOO. All classes are instances of this class. Consequently, oo::class is an instance of itself.
? oo::object ? oo::class
AMG: Is there a compelling reason why [oo::class new] is hidden?
DKF: Because everyone treats classes as named entities with long lifetimes. Expose it if you want.
AMG: How do I do this? Sorry, I'm a total TclOO newb. :^)
DKF:
oo::define oo::class export new
Note that this does it for all classes. It might be better to do this instead:
oo::define oo::class self export new
This only exports it for oo::class itself.
AMG: Can I define a destructor for a class? Automatically deleting all subclasses, instances, and "mixees" is good, but I'm working on a project that needs some additional cleanup when a class is destroyed.
DKF: Yes. The simplest technique is to make your class an instance of a subclass of oo::class and attach the destructor to that.
oo::class create class-with-destructor { superclass oo::class destructor { puts "bye!" } } class-with-destructor create MyClass { # ... }
But if you've already got your class instance, do not despair! You can inject the destructor through modifying the class instance's superclass with oo::objdefine:
oo::objdefine MyClass class class-with-destructor
If you're changing objects' classes, remember that classes cannot be changed to non-classes or vice versa, and both oo::object and oo::class cannot have their class changed (they're special, for the sake of sanity). (And this is something where a mixin won't work; mixins are currently ignored for destructor processing, and while maybe that shouldn't be so, it's how things are now.)
AMG: Wait a second, according to [L1 ], "the destructor is called when objects of the class are deleted". I want a destructor for when the class itself is deleted.
DKF: Yes. I know:
% oo::class create class-with-destructor { superclass oo::class destructor { puts "bye!" } } ::class-with-destructor % oo::class create foo { destructor { puts "killing [self]" } } ::foo % foo create bar ::bar % oo::objdefine foo class class-with-destructor % foo create bar2 ::bar2 % bar2 destroy killing ::bar2 % foo destroy bye! killing ::bar
Is that not what you want? (Note that class destructors are processed before instances; guaranteeing order to be the other way is somewhat tricky…)
AMG: No, it's not what I want. I want to schedule code to run when [class-with-destructor destroy] is invoked, or the class is destroyed by other means (e.g. rename to ""). I have external data associated with the class (not the instances), and that external data needs to be cleaned up when the class goes away.