oo::abstract — a class that does not allow direct instances of itself
package require tcl::oo
oo::abstract method ?arg ...?
oo::object
→ oo::class
→ oo::abstract
Abstract classes are classes that can contain definitions, but which cannot be
directly manufactured; they are intended to only ever be inherited from and
instantiated indirectly. The characteristic methods of oo::class
(create and new) are not exported by an instance of
oo::abstract.
Note that oo::abstract is not itself an instance of oo::abstract.
The oo::abstract class does not define an explicit constructor; this
means that it is effectively the same as the constructor of the
oo::class class.
The oo::abstract class does not define an explicit destructor;
destroying an instance of it is just like destroying an ordinary class (and
will destroy all its subclasses).
The oo::abstract class defines no new exported methods.
The oo::abstract class explicitly states that create,
createWithNamespace, and new are unexported.
This example defines a simple class hierarchy and creates a new instance of
it. It then invokes a method of the object before destroying the hierarchy and
showing that the destruction is transitive.
oo::abstract create fruit {
method eat {} {
puts "yummy!"
}
}
oo::class create banana {
superclass fruit
method peel {} {
puts "skin now off"
}
}
set b [banana new]
$b peel → prints 'skin now off'
$b eat → prints 'yummy!'
set f [fruit new] → error 'unknown method "new"...'
oo::define, oo::object
abstract class, class, metaclass, object
Copyright © 2018 Donal K. Fellows