- NAME
- oo::class — class of all classes
- SYNOPSIS
- CLASS HIERARCHY
- DESCRIPTION
- CONSTRUCTOR
- DESTRUCTOR
- EXPORTED METHODS
- cls create name ?arg ...?
- cls new ?arg ...?
- NON-EXPORTED METHODS
- cls createWithNamespace name nsName ?arg ...?
- EXAMPLES
- SEE ALSO
- KEYWORDS
oo::class — class of all classes
package require tcl::oo
oo::class method ?arg ...?
oo::object
→ oo::class
Classes are objects that can manufacture other objects according to a pattern
stored in the factory object (the class). An instance of the class is created
by calling one of the class's factory methods, typically either create
if an explicit name is being given, or new if an arbitrary unique name
is to be automatically selected.
The oo::class class is the class of all classes; every class is an
instance of this class, which is consequently an instance of itself. This
class is a subclass of oo::object, so every class is also an object.
Additional metaclasses (i.e., classes of classes) can be defined if necessary
by subclassing oo::class. Note that the oo::class object hides the
new method on itself, so new classes should always be made using the
create method.
The constructor of the oo::class class takes an optional argument which,
if present, is sent to the oo::define command (along with the name of
the newly-created class) to allow the class to be conveniently configured at
creation time.
The oo::class class does not define an explicit destructor. However,
when a class is destroyed, all its subclasses and instances are also
destroyed, along with all objects that it has been mixed into.
- cls create name ?arg ...?
-
This creates a new instance of the class cls called name (which is
resolved within the calling context's namespace if not fully qualified),
passing the arguments, arg ..., to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). If the constructor fails (i.e.
returns a non-OK result) then the object is destroyed and the error message is
the result of this method call.
- cls new ?arg ...?
-
This creates a new instance of the class cls with a new unique name,
passing the arguments, arg ..., to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). If the constructor fails (i.e.,
returns a non-OK result) then the object is destroyed and the error message is
the result of this method call.
Note that this method is not exported by the oo::class object itself, so
classes should not be created using this method.
The oo::class class supports the following non-exported methods:
- cls createWithNamespace name nsName ?arg ...?
-
This creates a new instance of the class cls called name (which is
resolved within the calling context's namespace if not fully qualified),
passing the arguments, arg ..., to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). The name of the instance's
internal namespace will be nsName;
it is an error if that namespace cannot be created.
If the constructor fails
(i.e., returns a non-OK result) then the object is destroyed and the error
message is the result of this method call.
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::class create fruit {
method eat {} {
puts "yummy!"
}
}
oo::class create banana {
superclass fruit
constructor {} {
my variable peeled
set peeled 0
}
method peel {} {
my variable peeled
set peeled 1
puts "skin now off"
}
method edible? {} {
my variable peeled
return $peeled
}
method eat {} {
if {![my edible?]} {
my peel
}
next
}
}
set b [banana new]
$b eat → prints "skin now off" and "yummy!"
fruit destroy
$b eat → error "unknown command"
oo::define, oo::object
class, metaclass, object
Copyright © 2007 Donal K. Fellows