Dear Krzysztof,

Good example, no easy answer! When you create an object b1

B create b1 -foo 10

your goal is most probably to chain the assign methods of the slots foo of the classes A and B along the precedence path of the object b1.

The simple but unsatisfying approach is to call the "right" assign method manually:

=========================================== Class create B -superclass A -slots { Attribute create foo -proc assign {domain var value} { if {$value < 0} { error "Value cannot be less than 0" } ::A::slot::foo assign $domain $var $value } } ===========================================

This crude approach will work, but is unsatisfying, since the "assign" method of class B has to know that the superclass of B is A and it has to know, that the same-named slot of class A exists and has as well an assign method.

In the approach below this information is obtained via introspection by a method named "continue", which is supposed to be quite generic.

=========================================== Class create B -superclass A -slots { Attribute create foo -proc assign {domain var value} { if {$value < 0} { error "Value cannot be less than 0" } my continue $domain $var $value } } ===========================================

Below you will find the implementation of method "continue". Note that there will be some changes in this are in XOTcl 2 and NX.

hope this helps -gustaf neumann

=========================================== ::xotcl::Attribute instproc continue {domain var value} { set order [$domain info precedence] set current [[my info parent] info parent] # # find the next class from the precedence order # for {set order [lassign $order c]} \ {$c ne $current && $c ne ""} \ {set order [lassign $order c]} {continue} # # iterate on the remaining order until we find next # assign method foreach c $order { set slot ${c}::slot::$var if {[info command $slot] eq ""} continue if {[$slot info methods assign] ne ""} { # # invoke it # return [$slot assign $domain $var $value] } } } ===========================================

On 05.01.11 15:50, Krzysztof Frukacz wrote:

Hello,

I have a question for which I haven't been able to find the answer. I have two classes:

Class create A -slots { Attribute foo -proc assign {domain var value} { if {$var > 5} { error "Value cannot be bigger than 5" } $domain set $var $value } }

Class create B -superclass A -slots { Attribute foo -proc assign {domain var value} { if {$var < 0} { error "Value cannot be less than 0" } #I don't know how to call assign for foo in class A here } }

What I want to to is for assign proc from B to call assign proc from A too check both conditions. Thank you for your help.