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

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class identity {#class-identity}

An identity expresses that Attribute A of object O1 equals Attribute B of object O2. It is the most basic relation object.

Instance variables {#class-identity-instvars}

• identity<->from: selector1=name Attribute at the specified side of the constraint object. For normal bi-directional relations, both constrained objects should define both send- and get-behaviour with the specified name.

  If a constraint object is used as a propagator (see `constraint ->initialise'), get-behaviour on one side and send-behaviour on the other suffices.

• identity<->to: selector2=name Inherits description from: identity-from

Send methods {#class-identity-send}

• identity->backwards: from=object, to=object Performs a get-operation on to using the selector <-to, followed by a send-operation on from using the send <-from.

• identity->create: from=object, to=object Update after instantiation.

• identity->forwards: from=object, to=object Performs a get-operation on from using the selector <-from, followed by a send-operation on to using the send <-to.

• identity->initialise: selector1=name, selector2=[name] Create a relation defining

  ``Attribute selector1 of `constraint <-from` equals
  Attribute selector2 of `constraint <-to`''
  

  If the second selector is not specified is defaults to the first.

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