| abstract(3tcl) | TclOO Commands | abstract(3tcl) |
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"...'
abstract class, class, metaclass, object
| 0.3 | TclOO |