abstract(n) TclOO Commands abstract(n)

```

```

# [NAME](#NAME)

oo::abstract - A class that does not allow direct instances of itself

# [SYNOPSIS](#SYNOPSIS)

```
package require tcl::oo
oo::abstract method ?arg ...?
```

# [CLASS HIERARCHY](#CLASS_HIERARCHY)

```
oo::object


   → oo::class


       → oo::abstract
```

```

```

# [DESCRIPTION](#DESCRIPTION)

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**.

## [CONSTRUCTOR](#CONSTRUCTOR)

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.

## [DESTRUCTOR](#DESTRUCTOR)

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).

## [EXPORTED METHODS](#EXPORTED_METHODS)

The **oo::abstract** class defines no new exported methods.

## [NON-EXPORTED METHODS](#NON-EXPORTED_METHODS)

The **oo::abstract** class explicitly states that **create**, **createWithNamespace**, and **new** are unexported.

# [EXAMPLES](#EXAMPLES)

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"...'
```

# [SEE ALSO](#SEE_ALSO)

[oo::define(n)](/man/os/tcl/oo::define.n), [oo::object(n)](/man/os/tcl/oo::object.n)

# [KEYWORDS](#KEYWORDS)

abstract class, class, metaclass, object

0.3 TclOO

---

Document: oo_abstract(n) from tcl 9.1.0-r1 (Chainguard OS)
Source: https://downloads.sourceforge.net/project/tcl/Tcl/9.1.0/tcl9.1.0-src.tar.gz