---
name: "oo_abstract"
section: "3tcl"
platform: "linux"
package: "tcl9.0-doc"
version: "9.0.1+dfsg-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/oo_abstract"
---

# oo\_abstract(3tcl)

a class that does not allow direct instances of itself

```

```

## NAME

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

## SYNOPSIS

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

## CLASS HIERARCHY

```
oo::object
   → oo::class
       → oo::abstract
```

```

```

## 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

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

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

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

### NON-EXPORTED METHODS

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

## 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

oo::define(3tcl), oo::object(3tcl)

## KEYWORDS

abstract class, class, metaclass, object