src/swipl-devel/packages/xpce/man/refmanual/md/constant.md

In rswipl: Embed 'SWI'-'Prolog'

class constant {#class-constant}

Instances of class constant represent unique values. This uniqueness is represented and guaranteed by the object-reference.

Class constant defines the instance variables <-name and <-summary for documentation purposes.

The system defines the following constants:

| @nil     | _Nothing, not-filled_ |
| @default | _Use default value_   |

The user may create constants for a specific application. Constants may not be deleted as they are automatically protected using ->protect. See also class bool.

@see class bool

Instance variables {#class-constant-instvars}

• constant<->name: name Name of the constant. Note that <-print_name (used by class text_item) returns <-name by default.

• constant<->summary: string* Short description for documentation purposes. Similar to `class <-summary', etc.

Send methods {#class-constant-send}

• constant->initialise: name=name, summary=string Create a constant from its name and summary. The corresponding slots are filled and the created instance is ->protect'ed against the garbage collector. It is very uncommon for application programmers to define new constants.

rswipl documentation built on June 16, 2026, 5:07 p.m.